I’m speaking from purely from my own experiences when I ran a bike shop. I can’t comment on each individual shop, as we are all aware some are a bit less willing to bend the rules.
As I said, ask nicely. Most bike shop staff are pretty understanding and generally willing to lend a hand, as long as you’re polite. It’d be a different case if you’d bought a bike elsewhere that had cracked, and demanded that a shop strip down, send away, and rebuild a bike for you.
In a situation similar to, I think I charged the guy all of a fiver to cover the time it’d take to package up and then the cost of postage. For how long it takes, it’s no great shakes really.
Fair enough, they’ll probably not make any money out of processing it for you, but they may well take the same, longer term view that I did.