shockwave, it's hard to "try before you buy" with firearms. Like you, I seriously research most everything I buy. However, sometimes what looked good on paper doesn't feel so great at the range or in my holster, or maybe accuracy or reliability isn't where it needs to be. That's when selling a gun comes into play, especially if it's not something I want to tinker with or spend lots of money on it for gunsmithing. I know that some would never part with a firearm, but I personally will not keep something in the gun cabinet if I don't like it. It's better to put my money into something else.
That, actually, is the other reason I'd sell something. Sometimes I can't get something new that I want without parting with something I already have. There's finite money in the bank and space in the gun cabinet. So, sometimes something gets sold. If that's the situation, though, I think long and hard, as this is the scenario which can most often lead to regrets.