I've been buying on eBay for almost 9 years. Never had a real problem of note. You just have to shop smart and always ask how much shipping is before bidding (if it is not stated). The current trend with sellers is to "gouge" on (charge excessive amounts for) shipping.
Sellers do this to minimize the amount of money they have to pay to eBay.
I recently won a kit for $1.55. I know the seller did not think he got what he expected. He then sent me an eBay invoice for $14.30 parcel post shipping and a mandatory $1.35 for a total of $15.65 to send a model via slow boat from a town less than 200 miles away. This did not include the final bid price of $1.55.
I told him to send me a realistic shipping amount or I would report him for excessive shipping. I promptly paid the $1.55 for the kit by PayPal. I told him he would not be able to claim that I never paid for the kit.