I dont think it's that unusual that he doesnt want to assemble your parts.
No different than taking your pickup in for repairs but bringing the parts along.
A little different with guns and probably a auto shop. If you have high end auto parts and it is not a dealership and local shop i am sure they would put them in. But even the local shop will not put on inferior parts.
Likewise goes for firearms parts. You bring me a Kriger Barrel, Impact/Defiance Action We will chamber for you depending on the caliber and twist rate. Even if someone brings us the BEST of the BEST components and they don't match for the caliber to the action or the twist rate is off.
I would ask what their expectation is for the build and then say if it is doable and what results they may get. Would not want to put together a rifle with the d components and then completed the rifle would not shoot due to a caliber rifle twist miss match.
We recently at the end of 2022 had some friends want us the take older WWII rifles and make them into something they were not. Now some of these older rifles can be made into beautiful Sportsters., But can and a lot of work involved trying to get back to original worth woodwork, Bluing hard cast and Case Hardening. A lot of processes gone due the cost and EPA Reg., Does anyone know how hard it is to set up tanks of chemicals (that are really expensive) to "BLUE" a firearm and parts, every part has to be degreased, cleaned, and highly polished. Same goes for the rifle barrels and action, Now we are doing Creskoating. The setup is very expensive, the cerakote is very expensive, the equipment is expensive, the schooling to cerakote is expensive. THEN ALL THE COSTS OF DUING BUSINEES, Taxes, Licensee, Building Rent, FFl, EPA shipping and a dozen other costs.
We do it for the fun and being able to make our oun firearms and not put up with other GS. Never make any money. We give our more free services just to help the community.
Anyone getting into GunSmitting now and thinks they are going to make a million dollars has to have at least $2 million in the bank to start so when they loose the first million they have the second to fall back on.