My best advice for selling is to check out eBay and sort by sold and price. Remember that just because someone is asking $1,000 for a marble doesn't mean it's worth that. I'd say 90% of what you see for sale on eBay is overpriced and misidentified. Learning to ID marbles correctly takes years. Very, very few cats eyes, clears and solid colors are valuable, but not all. Another tip when you buy a lot to sort, if you see more than two of the same marble, they are very likely not worth a whole lot. Good luck.