The average guitar player probably doesn't pay much attention to the frets and might not understand some of the important factors that go along with a quality fret job. The first thing I will tell someone is the frets are the playing surface and therefore the condition of the frets is a major part of how well the instrument plays. The day to day reality of metal on metal contact between strings and frets means eventually frets wear out. A fret dress is a process where all the frets are leveled with each other and any pitting from the strings would be removed. Once they're level the tops of the frets need to recrowned into a nice round shape. Only a hint of a flat spot remains but once they're polished out the fret generally won't show the landing.
If the frets are simply too low they will need to be replaced. This is the time to correct any problems in the fingerboard so the guitar plays as good or better than when it was new. Any number of reasons can contribute to a fingerboard that is far from perfect but by removing the frets we're able to get the condition exactly where it should be.
For the player arguably the most important thing to consider is the size of the crown. There are a variety of different heights and widths to choose from and if you aren't sure what you'd like put in, play some instruments at the shop you go to and ask about the frets. If you're talking with an experienced lutheir it's likely easy to have them measure what you like so they make sure the new wire will be right. A taller fretwire can be a nice choice because over years of playing you'll be able to have more dressings done before having to replace them again. However, if you've never played a guitar with tall frets and you tend to press pretty hard it might sound like you're out of tune. Your fingers will be on the string and not really supported by the wood. It can be a little bit like a scalloped fingerboard. So take some time to play a few guitars and see what you like.
Once you decide what you like there will be a few more considerations before determining the exact wire. The process of cutting fret slots into the wood makes the material more flexible (less stiff) than it was before. Putting in wire which has a smaller tang than the slot will leave the neck less stiff as it should be. Perhaps you'll even hear a difference in tone but over years of string tension the neck might settle into an upbow the truss rod (eventually) won't be able to fix. These are things the tech needs to be sure of but as a customer bringing it can't hurt to have the conversation.
Aside from the wire itself perhaps the fingerboard radius could be changed as well. The radius of the fingerboard refers to the curvature across the fingerboard from one edge to the other. Vintage Fender guitars have a 7.25" radius while Gibson electrics have a 12" radius. Some vintage Gibson guitars will have something closer to a 10" radius. To me as a player a tighter radius is more comfortable to play than a flatter radius but this is personal preference to a large degree. Martin acoustics have a 16" radius and classical guitars will have a 20" or even no radius at all. The problem with the vintage 7.25" radius is at times bending notes is problematic because as the string is bent it moves into the middle of the radius and the string will have no clearance to vibrate. The note will die out or buzz when the string is bent. Combine that reality with any sort of shim or neck-tilt adjustment common to these instruments and the problem becomes even worse. Skillfully leveling the frets can eliminate the problem without changing the original radius. On a maple fingerboard with a finish this is a great alternative assuming there aren't other problems in the wood that need to be addressed.
Nearly every refret will mean the nut has to be replaced as well. The new frets are likely going to be too tall to work with the original nut slots. Some shops include this in the cost of the refret and others will add it on as a separate item. No matter how it's billed, realize it's likely going to need the work and it isn't just someone looking to make more money off the repair.