Only thing I'll warn you about is the "15 minute rule" which is one of the stupidest scams known to man. Generally I look for guns with a "Buy It Now" option, weigh the value of the BIN price, and if it fits in the box, buy it. Now. Almost never have I seen a gun with a 15 minute rule go for less than the BIN price...
Pay attention to how they accept payments as well. Some will only take one form of payment. Some will take credit card but tack on an extra 3%, etc...