This article is from the eBay FAQ, by William B. Shaw email@example.com with numerous contributions by others.
Pay promptly. If for any reason, you are going to have trouble paying,
contact the seller to make arrangements for a delayed payment. Many sellers
react better if they know what is going on up front and aren't being strung
along. With that said, the buyer is obligated to fulfill their obligation by
paying and the seller might, rightfully, leave a neg no matter how good you
think your reason is.