My attitude is influenced by the high prices charged by charity shops for fairly ordinary worn clothes. It used to be that people going through a hard-up phase would be able to clothe themselves for work, etc., at a very reasonable price. Now, in London, blouses are £8, skirts £12, etc, and ironed to look good, but actually a bit washed out and floppily thin. Outer clothing, such as coats, are often the only items in very good, thick and firm condition.
So, the shops make the profit by charging a lot for all types of thing. What you made was nice, but not like the apocryphal stories of a collector buying a Victorian bird painting which turned out to be work 66 grand. ( True story).
If your windfall was really big - into thousands - it might be nice to give some back to the shop. If you were a dealer, you'd say your gain was payment for the expertise and know-how which has taken you years to acquire via hard slog round antique fairs and car boot sales.
Maybe the people who bought your stuff on eBay were muggins, and the shop charged the right rate for what the things were, and you chanced your arm a bit and found somebody without a clue who either liked the things a lot, or wanted to be a dealer - and got it wrong.
Anyway, you've given the charity shops some publicity with this post, and I'm sure many readers will decide to mosey round their local Cats Protection League shop, etc., in the hope of emulating your success.