sales are as good as ever. Other sources I participate in outside of eBay
have seen no slow down in stamp prices whatsoever because of COVID-19.
It's true that the large majority of auctions on eBay
are posted as BIN's and are generally high priced, but not always. Also, a lot of them accept offers.
I've also noticed well known sellers with their own websites post material on eBay
heavily discounted from the list prices on their own websites.
High end stamps are competitive when auctioned - they go for relatively high prices but are still generally below what some sellers want as BIN or on their own websites.
I really doubt eBay
is shill bidding on auctions. I liked it better when you could see the username of the person you were bidding against, and I forget why they started masking them. Before that, for a variety of collectibles, there were cases where the same username was consistently bidding up one seller's auctions but never winning, and if they did win the auction ended up be relisted - which is suspicious, but not eBay
The eternal question of where new collectors will come from persists, but I doubt anything has changed in the last year. There was a good post on social media by a younger seller that drummed up a lot of attention pointing to stamps as a cool collectible - not dead yet.