For me, this dealer's style doesn't inspire investment, just based on those listings Parcelpostguy posted. The 359 he discovered, seemed like an accident based on his description and his 25k ask is a pipe dream. It's not happening, and certainly it is not an enticing fish in the tank, by any stretch for a buyer doing even the slightest bit of due diligence.
For the 233a, far better sold at Siegel in NH quality. Hard to think someone will plunk $8k on the bay, without googling 233a or make some calls to dealers who probably each have a copy and shop around. If you are hunting down high end Columbian's in the first place, you probably aren't starting your search on
ebay. They are hardly scarce (albeit a rare stamp), but the cert from 1980 shows 2 more issues, ambivalence, and subsequently raises the question, was the stamp recertified and failed using more modern color techniques and a newer cert discarded? Could totally be legit, but it's an exercise now left for the buyer. Not the type of dealer I would want to interact with.
Then we get to the invert. Here we have regum, and altered. Again, not the type of material I like to even entertain, although the disclosure does show a level of honesty. I get that there are people who would want to own a 296a invert (which this isn't), at a dirt cheap price, but the ones on
ebay, are not competitively priced in the slightest. Note this should be priced as a specimen. Yea, a gum intact one is way more money, but c'mon, a specimen removed is just a flagrant alteration on the stamp, and is a bottom fish for the 'invert at any price' crowd. The Arthur S. Przybyl had a modded invert, specimen that went for 4k at siegel.
In short, wouldn't go near this investment, if that wasn't obvious by now.
Personally I hate the model of buying problematic stamps sold to non-discriminating buyers. I get it. It's not my thing.
As an investor I would be more comfortable with a Rupp model of high end stamps with high end clients and many more advantageous avenues outside of hawking busted wares to
ebay pawns.