Fortunately I have had good experiences with buying and selling.
As a Buyer, I give feedback PROMPTLY after receiving the notes and confirming the grade that it claims to be. It is important to leave feedback AND contact the seller via Message or E-Mail to tell them everything arrived ok and you are satisfied. This makes things more personal. Buyers who do not feel like leaving Feedback is a level of disrespect as well. Let us not forget in the Currency Community is not huge so everyone knows everybody.
As a Seller, Communication is EXTREMELY important. I make an effort to always go the extra mile in communicating with the buyer, making sure they know the differences in shipping and the risks involved. Some People do not mind the risks of Regular mail but once it is $100 or more I draw the line and for everyone's safety I only ship Xpress. After the Buyer leaves me feedback and usually sends me a PM or E-Mail that they were happy I then do the same. Again, I do not leave feedback until I hear from the buyer. I feel this is the proper sequence of a transaction. I only had 1 person say they would not leave feedback until I did but everything went smooth so there was no concern.
As a seller it is
VERY important you build trust with your buyers. They will trust your grading of notes, quality of the product and know they can trust everything will go smooth. I have quite a few people who consistently buy from me because they are ALWAYS satisfied with the product (Either meeting or exceeding their expectations) and appreciate the extra level of communication.
As with Buying in person from a dealer or online, you must build a Buyer/Seller relationship. This Trust that you build is the corner stone of expectation for that transaction and possible future transactions.
I agree that there are some sellers out there who are more concerned about their feedback then actually making sure the customer is satisfied in the first place....