No, there isn’t any more risk buying a mining card than any other used card. In both cases you should use a platform/marketplace with buyer protection options. Maybe one additional step is checking the VBIOS when testing.

The non XT is the best value of the 6600 family but depending on local pricing the 6600XT, 6650XT and even the 7600 could make sense. Just keep in mind that these are the same performance class. Some charts show the mentioned GPUs.