don't blame the fitter for not fitting it TBH.
if something went wrong you would be the first to try a sue him.
at the end of the day your runing the tyer out of manufactuer specks so in therory all it certifaction is null and void so is it still even legal for road use ? also should it suddenly pop and you spin out on a corner and flatten a bunch kids waiting for the school bus, thats going to be one expensive claim on your insurance company, if they think they can get out of this they will. so ether you get sued, or they payout and then hit you for it.
whatever happens if something goes wrong, someone is going to loose all the money they have saved and all the money they havent yet earned.