Leaving positive feedback to a seller is very important.  Not only leaving positive but rating the seller using the star system. 

If you give him one or two stars because it arrives in six days and you think it should have arrived in two days, it will raise the rate he pays eBay on his future sales.  It could have been the UPS or the post office's fault.    I am not a vendor, but this is very unfair and hurts us buyers as well as the sellers. I have ordered several items from China and Russia with good results, but it takes a little longer to get them so allow for it.

Another suggestion is to not leave feedback on an item until you made sure it performs as described.  Do not just leave positive feedback because you received the item you purchased.  I have done that on a Computer mouse described as "Nearly New", only to discover the item was well worn, broken and beyond repair. Try it out for a few days before leaving feedback.  After leaving feedback, you have no bargaining power if the product is not as described.

I hope this helps someone......Happy eBaying.