No way! Sorry Matt, I've done a lot of transactions as well. I'm not handing some stranger an envelope with $$$ in it before we go in the store. I want the store to have his ID so at least I know who I'm dealing with if it goes south. I've never had an incident but an unscrupulous seller could literally "take the money and run".
I had a seller show me an (off roster) gun in the parking lot while he sat in his car and I was outside the window. I said "looks good" let's go inside so I can examine the gun closely. He had parked kind of far from the entrance and wasn't replying to my texts on the way to the meet. It feels sketchy to me to conduct business in the parking lot beyond showing me the gun, although I have done it once or twice. This guy happened to be LE, and I think maybe his first transaction, but he was cool and came inside.
Personally I want to:
1. Examine the gun inside
2. Start paperwork (most sellers are cool with handing over their ID so the FFL can start while I examine)
3. ASK the store if it's ok to exchange money inside
4. If ok, hand over the cash, if not step outside
5. Complete paperwork
Some sellers are totally cool with payment outside after the DROS is complete, maybe because they already have all my ID and info.
One time we completed the DROS before I payed, we went outside and I was so engrossed in the conversation, I didn't realize I hadn't payed him yet!. He had this puzzled look on his face and then it dawned on me, OMG I haven't paid! I apologized and handed it over immediately! Pretty embarrassing