I never sold our bought anythimg on Ebay, but I work for a company that sells a lot at amazon.
Their rating system with the sellers is like this.
5 stars: Nothing to celebrate, you didn't do anything less than we expected.
4 stars: WTF are you doing, idiot? Four stars? that's horrible!
3 stars: WOW! you need to die and reborn, maybe it may fix you.
2 stars: why do you still breath?
1 star: Nuclear holocaust
The worst thing that can happen is when a customer leaves a review with something stupid like that "The product is great, but I won't give five starts because when i had to call customer service, they let the phone ring THREE times instead of only one before picking up my call."
The "algorithm" will place a hold on your seller account, you will be invisible for other shoppers until you provide a series of documents to proof that you hired a third party company to trains your employees to pick up the phone before it rings or maybe take psychic classes and call the customer before he starts dialing your number, plus the call log for the last 10 million calls, including those from before Alexander Graham Bell was born, photos of all the phones and phone jacks in the company, and a letter signed by AT&T (all of the employees including the janitor) stating that your phone line is 100% ok and you will never miss a call again, plus a video with all of your employees learning how to use superglue to keep themselves stuck in their desks and also a receipt of the diapers the company purchased for the employees so they won't have to go to the bathroom.
Amazon is EVIL with their sellers. If possible, always try to contact the seller directly without using the Amazon mail system.
Amazon is so picky that, if a customers sends us messages using their system making questions about the product BEFORE THEY BUY IT, the system will put our account on hold because our product doesn't have sufficient information and that increases the data traffic, overloading their system.
Other thing people don't know about amazon.
Seller cans NEVER raise the price (even if our cost is higher). But all the time they send us a lovely notice that they will have to increase their margins because their operation costs is higher. It means we will be paid even less for our products. but we can NEVER raise the price if our cost is higher.