A dealer should:
1. know what they are selling. Sappire crystal, movement...
2. correctly present the advertised item.
3. be honest.
4. deliver the product in a timely manner. A may-not-be-working tracking number is better than no tracking number.
5. reply emails in a timely manner.
6. give the buyers the benefit of doubt. Murphy's law states "Whatever can go wrong, will go wrong." It's not always due to buyer's stupidity when things go wrong.
7. try to find a mutually beneficial solution when things go wrong.
8. look for long term relationship. Don't get personal. It's just businesss.
my 2 cents.
I recommend Andrew, Joshua, EL, river, King, PT, and silix-prime.