What exactly do you see when you open the page? I’m fairly certain sellers can’t decide that middleman accounts can’t bid on their auctions. You are not allowed to bid on these products because the middleman company had a ‘bad experience’ with the seller (Buyee is the one not letting you bid). This happens like @mrbubbles said if there have been complaints, or the seller refuses to sell the item for the winning bid. The complaint could of course be the result of sellers who refuse to work with middleman services on principle. Some accounts used by e.g. Buyee are well known by sellers and they can delete your bid.
Here an example. You can try if another forwarding service like ZenMarket does not have the seller blacklisted (although there often is a good reason for a block).