John Tye Piano Tuner
The obvious repair is a broken string. Some pianos never break a string, but we have to accept that it does happen, and sometimes during tuning. A good string can be raised more than a tone before it breaks, so I will not accept responsibility.
A tenor or treble string (plane steel) can normally be replaced on the spot, but, despite all efforts to stretch it at the time of replacement, it will still stretch and therefore drop in pitch over the ensueing weeks. The best solution is to tune it high and mute it until it has settled, but that is not always a sensible option.
A bass string (copper wound) needs making to specification so is likely to take a week. If the strings are old a brand new string might stand out. In this case it may be possible to repair the string by knotting a new end. It is recommended to replace both strings of a bicord, but I think that a bit of hammer shaping usually sorts out the inequalities of the strings.
Do not continue playing a piano for long with a broken string, especially a bass bicord. It will damage the hammer, and the twisting shock could damage its pivot (flange and centre) or even snap the shank.
These hammer felts are quite badly compressed. Nevertheless, if this is the first attempt they can probably be refaced. Compressed hammer heads have too much felt in contact with the string, which alters the harmonics. Refaced hammer heads have the original shape, so will give a better tone, but they are harder than when new so they will give a brighter tone. Toning (voicing, to moderate the brightness) is recommended for refaced hammers. I would expect to take the action away to reface. The piano will need regulating afterwards (including toning).
These hammers are beyond hope. One has been refaced just to show you the effect (the cleanest, and now the smallest, one), but if I did that to a treble hammer you would be down to the wood. So they need replacing. Again the action needs to be taken away, and the piano will need regulating afterwards.
Hammer replacement.
If your hammers have worn to the point that they need replacing, the chances are that the new hammers are going to be significantly longer and heavier. So, not only will the action need re-regulating to cope with the longer length, but the keys will need re-weighting to avoid an uncomfortably heavy action. This makes it a rather expensive business. I have included a basic replacement price that includes regulation, but uses basic hammers. The full price uses superior hammers.
A broken hammer shank can usually be replaced on site, but it is chargeable.
Loose tuning pins are a major cause of pianos going out of tune quickly. The wrest plank (the wooden support for the pins) wears and dries out. The offending pins eventually get so loose that the string cannot hold tune at all. Replacing the wrest plank is such a major job that large numbers of very loose pins spells the death of the piano. However, loose pins can be tightened as they occur. It can be done during a tuning, but it takes a while, so there needs to be time and I charge. There is a danger of breaking the string at the beckett (where it enters the hole in the pin), which would be your fault. If all pins are slightly loose they can usually be improved by a resin treatment, but it is not guaranteed to work, so I do it at just more than cost with no guarantee.

Just for interest, this is an Evestaff Mini drop-action piano (less than 3 feet high) in a pub having three loose tuning pins replaced.
The Keyboard
Very small chips on the key edge can be repaired. Replacing individual coverings can be difficult to obtain a match. This piano needs all the coverings replaced, which means that I have to take all the keys away for at least two days. You will need to consider whether you want a brilliant white glossy finish. This piano has off-white plastic coverings.
Ivories can be re-glued, but the join will always be visible. I have a small stock of second-hand ivories, but it is very difficult to find a colour and pattern match as well as a size match for any lost ivory coverings.
These keys from E upwards are leaning severely. These notes need to be hit hard, and they have gone out of regulation.
You can see that the felt has worn away on the left side of the balance pins, and F has split. The felt bushings need replacing.

The felt needs to be held in place while the glue dries.
A grand piano this time, with the hammers removed from the action so that I could extract this split F# key for repair..
The damage was caused by a corroding lead weight (removed)
Action repairs

This action was brought in because some notes could not be relied upon to play.
In the photo some hammers have been left in. These are the templates to help me re-align the hammers to the strings when I replace them. The final aligning cannot be done until the action is returned to the piano.

but present in this photo.
The tapes needed replacing, because otherwise I would have to try to re-install the action with all the treble levers drooping as in the photo above. It would be impossible to do that without causing some damage. (It is the damper springs that are holding up the lower levers, but not high enough without the tapes.)
Tapes do offer some help in pulling the hammers back ready to strike again, but the main component for this purpose is the butt spring, which is missing in the photo on the left (along with a broken tape),

A full action restoration would involve a lot more work including replacing the felt and leather. This photo shows badly worn leathers. One is on the verge of causing a noisy (clicking) action, while the other will already be causing unreliable holding of the hammer in check while the string is sounding.
This is the finished action. The butt spring is visible behind hammer butt number 31.

replacing plane steel string during tuning £10
replacing copper-wound string during the next tuning £35
replacing plane steel string close to Northampton (special visit) £35
replacing copper-wound string close to Northampton (special visit) £60
replacing a hammer shank on site £10
tightening a loose tuning pin during tuning £10
resin treatment for loose tuning pins during a tuning £60
replacing the bass strings - two days with an inoperable piano £520
replacing the hammers (basic) - at least four days with an inoperable piano £590
replacing the hammers and re-weighting - at least six days with an inoperable piano £980
replacing the rollers as well (grand piano) - another day with an inoperable piano extra £285
replacing the dampers - three days with an inoperable piano £345
recovering the keys - at least two days without the keys £180
rebushing the keys - at least two days without the keys £180
replacing the practice pedal felt £30
Action reconditioning.
The costs include regulation adjustments, so there are considerable cost savings by combining jobs.
Refacing hammer heads - at least two days without a piano action £120
Replacing all the tapes - at least two days without a piano action £140
Replacing all the butt springs - at least two days without a piano action £120
Any two of the above action reconditioning - at least two days without a piano action £170
All three of the above action reconditioning - at least two days without a piano action £200

These prices assume that the job is part of a tuning, otherwise add 25.