Alternatives to eBay abound if you're looking for sellers' websites, and often you can find things more easily there, with the process being better and the seller happy to do business with his buyers.
I agree that good communication is a must.
If an error is made, or if something goes wrong, sellers must put themselves in the position of the buyer. The buyer will probably be worried or concerned, and it doesn't take much (just a quick email) to reassure the buyer that the communication's been received and the problem is being investigated for quick resolution.