ForestCap
Well-known
As 36 or 37 lenses can be tested with a cassette of film I don't see that as an expense. And a lot of sellers in what was the USSR seem to have expensive digital cameras, even Leica M's.
RF lenses focus accuracy can be tested with a piece of ground glass or matte-finish tape sticking to the film rails of the camera, and lens sharpness can be tested by using digital camera. In this way it's even cheaper. But most FSU (eBay) sellers just don't have the attitude to do so. In best cases I've seen the sellers showed a picture taken with the lens on Sony NEX, but no more than that.