Learn then selling guidelines. Each marketplace has guidelines that define what you can and cannot sell. State and federal laws also impact what items are prohibited. In general, you cannot sell alcohol, weapons, service contracts, animals or event tickets. Also, while not always prohibited, you may find restrictions on how you can sell items in some categories, such as art, gift cards and coupons. eBay, Craigslist and Amazon publish these guidelines on their websites.
If you love to travel and find yourself randomly searching for airfare sales or browsing Lonely Planet, why not carve out a niche for yourself as a private travel agent? My friend, Mark Jackson did just that, making extra money online with his travel consulting side business. Start with word of mouth recommendations from friends who know they can count on you for the cheapest flights, and then move on and create a Facebook or LinkedIn group to invite people who want to stay on top of the latest deals. Eventually you could spin this into a full-time consultancy teaching people how to make their dream trip a reality.