What to do with replaced tweeters

Hi - so, not naming any brands or companies here, but about a year ago I upgraded my speakers by installing new beryllium tweeters. I still have the old and undamaged tweeters. However, I've looked on ebay and on here and on other audiomarts and there's none of this particular, mostly well-known-among-audiophiles tweeters (or woofers, for that matter) on the market. So, where does one sell unwanted tweeters? And how does one determine a value to set? Should I just keep them "in case"?

Again, not trying to make a sale here; but trying (perhaps ignorantly) to figure out what to do.

Warm regards,

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It is up to you but, if you ever think you may sell the speakers, I would keep them. Even though the new tweeters sound better, but most buyers want as much of the original speaker/component when buying. Just an opinion of course.
Depends also if the new tweeters are from the same company as the speakers and are part of the company's upgrade, rather than an after market product. If not, definitely keep the old ones.
Yes, the new tweeters are from the same company are part of that company's upgrade ladder on the speakers.
Didn't the manufacturer offer any type of trade in discount when you purchased the new BE tweeters? It seems he did offer that at some point Simao.