The difference between “lots” and 3900 is a lot, me thinks.
If it is truly successful for GM on the whole, I guarantee other will follow suit with their "Certified"s…
However, I don’t think it’ll be super successful. I think that alot of GMs Cert Used market are not the type to spend 10k via ebay. However, having a big name (GM) actively backing the program & publicizing it may help quite a bit.
With respect to eBay, having such a large recognizable “old industry” name like GM throwing its branding & weight into it would validate ebay for ALOT of fence sitting consumers who aren’t exactly early adopters.