I've been scammed on CL with fake bills before. Was a hassle and I end up loosing the money despite a police report, picture of the persons car / license plate and photo of them.
I now meet only at a police station, bank or university (as all have security and security cameras), check the bills with a counterfeit pen, view the serial numbers on the bills and if worst comes to worst, go inside the police station or bank to have them check. Rather be safe than have that happen again.
Fake money can go into an ATM and get processed (not normally but it does happen). Than you get a letter from your bank saying you gave them fake money. The ATM isn't perfect and can still accept fakes, but the money is checked again and they usually catch it with that check. Get a counterfeit pen at least or go into the bank, don't rely on the ATM alone.