Mystery of the eBay Overbids Solved?

I bought another gift certificate off eBay for barely under face value, which spurred me to ask the seller what I was wondering about in a post a few months ago: why do gift certificates often sell for above face value?

The seller gave me this insightful response:

Ebay issues discount vouchers to buyers like 5 % or 10 % off. So buyers bid upto $105. Depends upon the terms and conditions of the voucher and their necessity.

That seems to make sense.