Im not gonna lie, its sketchy for both parties. You just have to make sure you meet in a public location (store, bank, police station etc.).
I prefer bank or grocery store because I can check the money before i hand over the merchandise.
And never drive to them, if they want it, they will have to drive to you.
This guy tat I sold my 6 to had said it was a replacement for his phone until he got the 7+. When I met him, he said his son had broken his phone so he saved up money to buy a used one. he paid with $20's, $10's and$5's..
The sketchy part was that he did not get out of the car and he had his right hand tucked to the his right side of his body. I didnt say anything, I just greeted him and showed him the phone. He said perfect and handed over the cash. I counted the money, shook his left hand and walked away.
Even when he put the car in reverse, he used his left hand to switch gears. I dont know if he was hidin something or he was just handicapped. But not matter what, I was ready to limp away (had knee surgery).