At the risk of being off-topic, I am a firm believer of fixing/attempting to fix first before replacing so I'll point out how painfully easy it is to fix/replace the shoulder buttons.
The replacement process is
fairly straightforward, there is more or less no risk of screwing up anything important; the only thing you can really screw up is the L/R ribbon cables if you carelessly yank the bottom half of the shell off without disconnecting the L/R buttons' ribbon cables (against the guide's recommendation, and if you did mess them up, the replacements are so cheap it's not worth worrying about.) I guess you could also mess up by losing the spring or the pin somehow, but that can be avoided by being careful when taking it apart.
From there, you either
fix the buttons on your own (DS Lite guide, but the process if the same for pretty much all Nintendo handhelds as they use the same shoulder buttons), or if you don't feel comfortable with that process,
Amazon sells replacements for $7 (not sure about shipping but it seems you can get free shipping if you buy for at least $35 worth of stuff; useful if you already had other stuff to buy on there, otherwise you're better off just paying shipping.)
No soldering skills required, just two ribbon cables that you disconnect and replace. Worth learning your way around that sort of thing as lots of devices share similar technologies, and you can save a pretty penny fixing them on your own.
Don't get me wrong, I am not suggesting you cancel your order or anything (unless you really need the money); it can be good to have multiple systems at hand in case something goes wrong with one of them, then you can still use the other one. Although I do suppose you may be able to get some money back by selling your old one, or perhaps give it away to a relative if you felt generous.
(If anything, somebody else will have learned something today and saved themselves some money on buying a new system. ;p)
