I can fix most Macs. I have a few old macbooks that are waiting for parts to materialize on craigslist too.
Wireless should be pretty simple to fix. Either it detects accesspoints or it doesn’t.
If it does then it is configuration, if it doesn’t, it is usually the switch turned off (software on some) or an actual problem with the internal mini pci slot or module.
Tell us what model and if you detect signal then I (and probably a dozen people reading this blog) can probably tell you how to fix it.
If you insist on spending lotsa money on “authorized Mac service” for an older unit then goforit. The mac store could not stay in business without ya.
:)