Depends on the dealer, but more than likely, your economic misfortune is none of their concern. By that, I mean that if you throw $400 at a MAF, and it doesn't work, don't expect them to care that they just blew $400.
Now, they MAY be able to put a MAF in, and if it doesn't fix it, to pull it out and return it, but most parts suppliers won't take returns on electrical components, especially MAFs. Depends on the shop. I'd at least ask.
I would be very wary of continuing with the dealer, sorry I don't have any better advice. It sounds like they just want to throw parts at it until you give up, or they get lucky.