Sure, if you have a target game coming up, of course should wait.
For flashed card, there is only one reliable source. And won't be cheap.
For Official Mac card, they are even more expensive.
As you said, there is nothing hurt to study more. For Nvidia card, it's a bit more scary, but the flash process should be very straight forward (download and flash).
For AMD card, you have a little bit more choice (create the ROM by yourself and then flash it). By making you own EFI ROM, that will have best result on compatibility. That's a bit more complicated, however, since most 7950 have dual ROM design. It's basically error proof. Even tough you flash a bad ROM to the card, you can simply flip the switch, boot with the good ROM, and then flip the switch again (when the machine still running), then flash again and Replace the bad ROM with a good one. As long as you keep one ROM save (read only, but don't write on it), you are always safe to flash.
Anyway, either pay someone reliable to do it (IMO, that means MVC). Or do that yourself to save money. From the sharing in this forum, buying a flashed card from an unknown source has high chance to suffer from all sorts of different problem.
Since all flash procedure are well documented in this forum, I just can't see the point why pay a bit more (to an unknown source) and let yourself take the risk. The worse part is that the card may not even come with the original ROM, that will prevent you to fix the problem (if any).