Oh, maybe it's just me that was confused and did not understand your case. Let me fix that: you went to the shop for a diagnosis maybe expecting a simple operation and was told the computer requires unexpectedly expensive repair, so you bought a new one instead? I thought you knew it beforehand since it was old already.

In that case where there is no Apple sanctioned repair presence such shops either usually sell Apple hardware and gladly perform support and diagnosis if that can bring them a sale, or they're nice enough to help you anyway with the diagnosis out of good will (people are generally like that in digitally scarce areas) and will direct you to get a new one at the mall (or, they're dicks and then, screw them).

You have every right to call me an optimist about human behaviour though ;)