So you've finally upgraded to a Wii U, and you're ready to send your original Wii to a new home. What steps do you take before you send it off? And what are your best options for selling it?
First, make sure you read about transferring your data from your Wii to your Wii U. The link is at the bottom of this article. That ensures that as much data as humanly possible is retained. If you don't have a Wii U, and are accepting the fact that you'll lose the games and data that is currently stored on your Wii, then you'll want to go menu by menu through your Wii system and manually delete the items. That way whoever you turn the system over to doesn't have access to any of your data.
Make sure you open all the hatches and ports and make sure you haven't left any SD cards or other memory cards in the unit. If you do want to include them in the sale, make sure you remember to list them and to format / clear out the cards.
Next, you'll want to look at the various online systems to see how the sale prices are comparing. Check out ebay, Amazon, and craigslist in your area. Depending on where you live there could be higher or lower values for the various systems. Remember to factor shipping in to your costs, and to look at exactly what is being offered in the system. A system that includes controllers tends to sell better than a bare bones system, for example.
Also consider what system you have a well rated account in. If your Amazon account has a zero rating because you've never done a sale through Amazon, while your Ebay rating is doing quite well, then you might lean towards ebay for a transaction like this. People are sensitive about buying electronics from an untrustworthy source. If you really do want to use a source that you don't currently have a high ranking in, give though to investing some time in building that ranking up with less "risky" item sales. For example, if you really want to sell your Wii on Amazon, but you don't have any ratings yet in the Amazon sales system, sell some other inexpensive things first. Go through your library and sell a bunch of books. That way you build up your ranking with the books, and the people looking at buying a Wii will now know you can be trusted.
In the end, the real key is to get your data off, if at all possible, and then to wipe the system of all your personal information.
Best of luck!