Is it my imagination?

I think the spice trade routes and the Tea Companies were founded on this. Buy goods inexpensively in one market and sell it at a higher price in another. Sounds like a Free Market trade to me!

Yes it is arbitrage. I would think it is usually the other way. eBay seems to get higher prices most of the time if it is a well know brand. Rotel, B&W, NAD, MSB, Adcom, Nordost and high end Yamaha, Marantz, Onkyo, etc.

I've actually had dealers buy my used gear; and then it shows up on their website's used/demo page at more. The dealer usually offers a warranty on used/demo equipment, so they can get more $$, especially from walk-in customers. One in particular was a vintage 80s Cambridge Audio amp, back when they were still made in England. The dealer was a Cambridge Audio dealer. I think he was interested in comparing it with the current stuff. He sold it later. The rest were mostly Tuners.

I agree with the points made, and support the mechanism of the free market. On the other hand it misleads buyers who make offers in good faith and are either mucked about while the auction concludes, or stood up when the eBay bid price closes the margin. Personally I would post feedback if I believed I was misled in this way, simply to let others know that they should be aware of the seller's lack of authenticity. Free markets operate better with better information.

Actually eBay frowns on people who run an auctions and have it listed for sale elsewhere. They've delisted people for ending auctions early because they sold the item elsewhere.
Advertising an eBay auction elsewhere is OK, I am referring to a regular classified that does not disclose it is on eBay.

...that's exatly the way...