I'll casually keep an eye out for items for other attendees if I know a friend is looking for something, but as to actual purchase, not usually.
I did this once for a local friend who was looking for Boy Scouts Eagle Scout boxcars. He had been at the meet, but did not notice them. Since we live near one another, I called him and told him what price was being asked for them, and he was appreciative that I picked them up for him. There was very low risk in terms of it not being what he wanted though, being new production and a very specific item.
-Dave
