As much as they cause grief in many ways, eBay does have some limits intended to safeguard the marketplace. Certainly, big businesses get escorted when they enter the eBay realm, but for the faceless masses, there are defaults.
I know they have Seller limits - meant to limit how much a Seller can offer for sale at one time. This prevents some scammer listing 20,000 $50 items to hit the market quickly and disappear even faster.
I know they have transaction limits. A friend of a friend found an antique item on their property and initial investigations indicated it was quite valuable, so they put it up for auction on eBay. Bidding crept up to nearly $100,000 and stopped there. After the auction ended they were contacted by one of the serious bidders to say they tried bidding over $100k, but eBay wouldn't let them place such a bid. The bidder tried to get the limit lifted,, but the auction ended before anything could be done. What followed was nothing short of a shit fight from the "winning" bidder (including legal moves), but after all the facts were considered, eBay declared the auction invalid. Subsequent valuation opinions put the item's value as being at least $250,000. No wonder the "winner" was pursuing the matter.
Now I know there are buyer limits. It would seem these are meant to prevent a buyer going ballistic and beyond their means. A TEA pacemaker perhaps?
From what I understand, these limits can be altered, but it requires a call to eBay.