How are we supposed to anwser any of that? Unlike you, we have not seen the offer...

The AGS-001 model is not backlit. It has a frontlit display.
Personally, I have not heard of such a scam, yet.
Even if it does turn out to only be an AGS-001 screen, at half the price you should still get your money worth, I think.
The cost for such a mod should be around $60 maybe. ($20 for a GBA, $25 for a GBA SP (AGS-001), $5 adapter cable, 1 hour work)
Try picking it up personally.
Try paying via PayPal or Ebay.
Or just take the risk. If it is not a total fake, you would still be able to sell it on afterwards.