Maybe having a rating system would be helpful.
1. was the correct plant shipped
2. was the order shipped when promised
3. was the delivery on time(might not be the sellers fault)
4. what was the condition of the plant when received
5 did the plant actually live
6. were communications good during the transaction
Maybe some other feedback could add some more suggestions to the list. I have not had much experience with rating a seller, so I would also be interested and what criteria others use.