I'd say that about 93% of the forum deals I am involved in go smoothly, and about 7% end up comical or in disaster.
Once I had some parts I offered up - with the only catch being that the receiver sticks something in a medium flat rate box and send it to me. I was easy, anything consumable in the garage - pens, pencils, beer, smoked meats, sockets.... I didn't care as long as it went in a box and made it back to me. So the guy on the other end of the country bought some really nice expensive smoked fish (that needed to be refrigerated), stuck it in a flat rate box and sent it off. When I got it I just shook my head, but I wasn't specific enough about needing the smoked meat to be nonperishable...
Another time I did a deal where I purchased a cheap part on eBay for a fellow overseas where the seller wouldn’t ship outside the US. I then shipped it overseas and gave the guy the bill for the part plus shipping....Never ever got paid, and the guy never surfaced again on the forum. Some metal band member in Europe (never anyone on 71-73).
I have also had a time where the simple answer "No" would have been fine, but the person who offered up the free item just didn’t communicate. I was in a jam and could have used the parts, responded promptly to the ad, then found out a week or three later that the free item went to someone else when the other person posted a thank you. Luckily the part I needed was graciously offered up by another member across the country and shipped to me. All was fine in the end, but it would have been nice if the seller would have just responded "No" at the beginning instead of leaving me in the twilight zone.
I know everyone has a life and a job, but if you put something up for sale I feel like the seller needs to check the forum often or just put a disclaimer up that it may take a week or so to get back to you.