It's like anything else.
Sometimes you get what you pay for, and sometimes you pay for what you get.
Some shops do only 'full race' set up to your suspension: special coatings, custom pistons, billet adjusters, etc.
They are going to be priced at the top of the scale.
Other shops have 'figured out' what works using the least amout of changes, for specific kinds of terrain.
I prefer a more local shop, or, a shop that caters specifically to the type of riding I do.
EG: you would not use ProCircuit for Enduro tuned suspension. Not that they are capable, but becuse it's not where the come from.
Stillwell, RG3, TBT, are some companies that do offroad tuning as thier core method of suspension tuning.
There are specific shops that do a better job with KYB for offroad than others.
....but the most important thing is the information you give them, so they know exactly what to build for you.
You have to be very specific about actual weight, riding style, and terrain type.
If you tell them you sit down most of the time, use a Rekluse, and are geared 12/51, you will get a different build from someone who tells them that you stand up all day, don't use a rekluse, and are geared 14/51.
I would talk to riders you come across who seem to have less struggle with their bikes about how they are tuned and by who.
If your YZ is 2007 or later, you have SSS suspension, and it can made to be anything you want; you just have to know exactly what that is.