i have myself done and know many many people who do "remap" cars, some successful and some not so but i know for a fact that everone of them has at least a basic launch diag machine or similiar capable of reading basic faults from a large veriety of cars.
Im always a little scepticle of people who claim to be "engine tuners" or "remappers" as the equipment is available to eveyone even those with absolutely no knowledge of cars, just buying the gear doesnt exactly make people capable of doing the job and i have seen the conciquences many a time where people take little care and quite easily **** up there customers ecu.
However i might be wrong about yourself and try not to judge. I'd be careful stating your a remapper in threads though as the mods can see this as advertising and ban you.
I've been there and done it when it comes to the motor trade - remapping, milage correction, key
coding, diagnostics, immobilliser removal the lot and have taken the knowledge away with me and now focus on my full time job so its not as though i dont know what i'm taking about but as boring as my job can be it keeps the kids in sweets and me in beer.