How can an individual access car auctions?

Seems like 95%+ of cars for sale on Craigslist & Facebook Market Place are by individuals who purchased the car from an auction & selling for a profit from their home. How are they able to get cars at dealer only auctions without being a car dealer? Years ago I could I could participate on non dealer nights at multiple car auctions in the Atlanta area. No longer the case. Ideas on getting into auto auctions to buy cars for friends & family? Thanks.