Constantly. If I see a good deal on something I don't really want Ill buy it to trade or resell. I generally end up selling em to friends for what I paid but sometimes I up sell or trade up on something I want.
There are guns I won't sell or trade for sentimental reasons other then that they are simply a commodity to me. No different then silver or gold where I try to buy low and sell high. I do try to hang on to things for at least a year just in case I decide there is a place for it in my collection. After that I cut it loose. I have some regrets yes. Most regrets are guns I passed up buying though. Not ones I sold or traded later.
Sorry Cheapshooter I am a bad grasshopper...