A completely credible eBay alternative is craigslist, and this web site fulfills a huge need in the world by allowing most posters to list items for free. It's a good eBay alternative because it is free, and it also has a huge number of visitors. However, unlike eBay, craigslist requires that you do all the work for the transaction, and you may only be able to sell locally, depending on your product.
The auction service, eBay, provides great tools for sellers, like instant links to paypal, and rates sellers by their user-reported reputations. They also provide buyer protections on high ticket items. As an eBay alternative, craigslist has the advantage in that it is free to list the item. Craigslist is home to many would-be scammers, and eBay is less so. Having tried to sell an expensive item on both, I can assure you that there are many people out there who make a living trying to scam by using money order and cashier check schemes.
If you get a response from someone on any eBay alternative, or even eBay itself, that says that they want to buy the item as is, but they are located offshore and will send a representative to your home to retrieve the item with a cashiers check or money order, and take care of the shipping themselves, you have been scammed. Do not give these people the time of day, but do report them to craigslist or eBay.