If the seller 'does not know anything about it' then there is no economic obligation for profit.
There is no obligation, but no impediment either.
Just pass it on to someone that knows what it is and can use it.
Or sell it to someone who knows what it is and can use it. Or sell it to someone who doesn't know but is willing to take the risk to invest their capital. Or sell it to somebody who knows how to market it.
There is no need to be a sucker and give it away.
The downside of you wanting a stream of free enlargers to somehow automatically find their way to APUG members to snap up for free is that it devalues every other enlarger that APUG members own, especially the ones that they are trying to sell here and elsewhere.
Now if a seller gave it a complete test, clean and or repair, or is able to confirm it will do what the seller wants it to do, then a profit is justifiable.
If people are only allowed to buy and sell at prices that are "justifiable", that is communism: a totally regulated command-and-control economy. No thanks. Selling an enlarger is nowhere close to gouging gas prices in an emergency, and even then there is lots of economic merit to a free market.
'Flipping' is a source of useless economic inflation. No good or service has been produced for the exchange of money.
Wrong. When someone flips an enlarger it is more likely to be marketed such that it ends up in "strong hands": in the possession of somebody who actually will use it.
A person selling to a flipper is likely to not be able to sell to anybody else due to their ignorance, in which case the enlarger is likely to end up stuck in a corner of a dirty mouldy shed and become useless after a decade of neglect. Thus the flipper is rendering a service to the seller and to the analogue community by marketing it in a much wider range of venues such that it comes to the notice of those in the community desiring an enlarger like that. To do so, the flipper must risk their capital. They can lose if they estimated the value poorly or estimated the market poorly or evaluated the condition of the enlarger badly.
Suppose you inherit an old rifle from an uncle passed away and you don't know anything, say, about old rifles. You'd be a fool to just give it away to a stranger and find out later that it was an antique French musket used in the Indian wars in the early 1700s worth $20,000. Your uncle would at least want you to sell it to a collector for $3,500, say. It wouldn't matter if the collector already had two others in better condition and flipped it for $10,000 to another collector who waited three years for the right buyer who paid $20,000. You got something more useful to you ($3,500) than an old rifle you don't know about.
The alternative is communism.