Best thing you can do is clean the fool out of it as soon as you get it home.

They usually pack those guns full of oil and cosmoline and other stuff you don't want in there. Get some simple green and dilute it with water and completely disassemble the gun and give her a good bath to get all that mess out of the gas system and especially they barrel. If you do it right the first time, you should never have an issue with it... but as soon as you shoot it... a lot of that crap will get baked on and baked in and it'll take a lot of work to undo it.