Will a small, smaller than dime size, fairly shallow ding on the seatube ruin the integrity of a frame?
My buddy is offering me a frame for a good price, but this is the only drawback. Thanks in advance.
Probably not. If its an aluminum frame I probably wouldn't go hucking it down any mighty downhill runs, but I'd happily ride it. If its a steel frame don't worry about it at all.
If its a steel frame, it isn't terribly difficult to fix, if you want. Sometimes you can even just lube up a long seat post, and then gently tap it down and use it to push the dent out. But if its as small as you say, I wouldn't worry about it, the frame isn't designed with that close of tolerances.
That said, don't pay full retail for the frame, and make a big deal about the ding, hopefully you'll get a good price.