The best tip I can give anyone is ask lots of questions! I always answer questions asap. And look at the shipping costs before you bid! It doesn't cost very much to ship a marble. I offer the cheapest shipping possible, or priority if someone wants it. Return policies. I won't bid on a marble if it is not returnable, and neither should you! (We guarantee our marbles, and will always let you return it if you're not happy with it!)  Make sure you read all of the ad. Don't skip over the 'important stuff' like shipping, etc. Lastly, read the sellers feeback! Are they a respected member of the marble community? Are they experienced in selling marbles, or are they new to it? We welcome emails asking questions, not only about our marbles for sale, but ANY marble related questions!