Like olaru, I focus on musical instruments. Mainly guitars and bass. And some watches.
As for selling, I think a lot depends on what you are selling and how much its worth.
Most selling sites take their cut, but tend to do it in different ways. So, eBay likes to double dip with PayPal, Amazon is pricey per month but IS a
standardized fee, and sites like reverb have fixed limits on their % that are lower than eBay (but have a smaller market).
Really, my personal annoyance is.. err.. *idiots* bidding on eBay. The amount of times I've seen bidding wars that bring the item WAY beyond what it
should cost is astonishing. Likewise, it seems like folks feel they must
be getting a good deal if, say, the headstock is broken on a guitar..
so will spend whatever is necessary to win. Frequently equal to the cost of a brand new one..
I think the trick in buying is finding the items that have somehow fallen through the cracks, as there is a dedicated audience for every market.
Conversely, the trick in selling is ensuring your items never
fall through the cracks using everything from nice, artistic and informative
shots to proper titles/description.
As long as your items don't escape notice, you are likely to get a good price selling them in my experience. When buying, its all about the opposite,
which can take weeks of looking as well as the seemingly rare ability to walk away
when the deal isn't right any more.
ETA: I also think trying to find a niche can be helpful, though not at all necessary. In my case, I do work on the guitars before reselling. So, ill
do a proper fret level, general setup, some body work, new strings (Elixir, always), and pack them with a cable, picks, sometimes a gig bag or hard
The proper setup and fret work alone is a pretty nice selling point.
edit on 30-3-2018 by Serdgiam because: (no reason given)