checking price of legacy uniques

i have a lot of low level uniques from 2015 that are legacy. i saw some collectors buy legacy uniques even if they aren't good items. how do i check price of these items?

list in a public stash tab, set tab to 1 mirror (or whatever). Hang out online alla time, see if anyone messages you. Lower price, repeat.

Depending on your motivation and how many you have, you can press alt to see if they have better or worse stats than the current version to see if they are worth keeping.
Prices are a tough one, because you either have to have something really good or find a collector.

Legacy items with item quantity are sought after because they removed some and replaced it with rarity (goldwyrm for example used to have up to 30 iiq).

Alt arts can have significant value.

GL

Some unique versions have a (very) different mod than the others.
And some of these can be searched for, but not all unique mods are available always.

Or as was answered already:
Just try it.

But I don't think there are so many collector's for ALL unique variants.
But 1 may be enough :-)