If you want the mech to guarantee their work, let them select the proper kits for the carbs. If you've made other modifications to the bike from stock, ask them if they will tune your carbs to those changes.
Ask them if they will make adjustment if you start getting fouled plugs and if they will charge you for that adjustment.
If you can't trust them to get the proper kits, then you can't trust them to do the job right, either.
Ask them what kits are best and what has worked well for them in the past.
And, if you can't trust them to do the job right. Why are you having them do the work?