Are you selling on ebay to make money or to enter a popularity contest where you get stars better than other sellers?

You should never expect to get, and keep, perfect 5s.

Some buyers only give 5 stars if a seller goes above and beyond, they consider a 4 perfectly reasonable for a run of the mill transaction and why shouldn't they?

The only ratings you need to be concerned about are ones and twos and you will see if you get any of them.

It could be one buyer who has only left a 3 or it could be several buyers who have left 4s, what difference does that make to your profit margin?

Why would you want to block buyers who have a proven record of making payment and leaving pos feedback just because you think you are perfect?

You can only get a true picture of your overall performance after you have at least 50 ratings, under that number the average is effected too greatly by single entries.