If it is opened and inspected in the store while one of the workers was there to watch you do it that is one thing, once it leaves the store there is no one but you to say parts weren't removed, broken or replaced with parts from another plane that may have had problems. It's normal for a lot of stores to have a no return policy once it leaves the store. I have one of three hobby shops I could get away with a return, the owner knows me and trusts me to be in his shop alone even when he goes out for something. The other two LHS don't have a clue who I am and there is no way they would allow a return after I took an ARF or Kit home.
Just the nature of the beast.