I would not necessarily reject it out of hand but: I would want to know what had been done to it and by whom with supporting paperwork if available. A 'home tune' could be OK but I would again need to know what had been done, by whom and see the rifle, and shoot it first if possible. I might add that buying from a known person e.g. established member on here considerably lessens the risk. Otherwise it is a bit of a lottery but the risk is lessened if you are confident you can sort out any problems. Same with auctions of course.
Cheers, Phil