I did get 20 out of 100 damaged stamps only twice (from 100+ letters received so far). The damage was so evident (scissor clipped edges, foxing) that they shouldn't have been sent at all. Otherwise, the rate of damaged stamps is quite low, like 3-4 per 100. I think this was discussed in past threads. This should be stated more clearly on the site, maybe a help button or a welcome mail with basic rules will do.