At the prices he started selling these at, it's not possible to make a bootleg for profit. Even if they were bootlegs, why these items? There are tons of gaming things that would be more lucrative to counterfeit. The much more likely possibility is that he is just selling multiples of games he doesn't have, but again, why not Nintendo games? In terms of rare Neo-Geo stuff, this is definitely the most obscure to bootleg. These are all much rarer than all other Neo-geo items of comparable price, there is just much less demand.
I don't think it's too crazy to think that some retailer had 10 (or however many of these he has) black and white games left over when the color versions came out, and they ended up getting lost in storage for 15 years instead of being immediately put on clearance.
To me, the most suspicious thing is that he keeps listing these in multiples of two. On one hand, this is a great business move to create a sense of urgency and sell stuff quickly. But if you don't know what you have and are just trying to get rid of stuff (cheaply, as he started), I would have though he would have just listed every copy he had at once.
I don't think that there have been 9 copies of the PAL B&W version of NeoGeo Cup '98 Plus sold on eBay in the past 9 years.
This is the exact same thing I told a friend when I mentioned this to him. NGC98 Plus is extremely rare, but there is also very little demand for it. If these are real (which I am think may be the case), I imagine the value will get destroyed. I bought one to check it out and compare to mine. I wish the systems he had were as relatively cheap, as I still need most of the colors.
If these turn out to be real, it's a good thing for fellow collectors. As a whole, these five games were very difficult for me to find. When I was getting them, the other four were still $50 games, but they were still a real pain to track down.