I sell electronics on eBay, then I go buy a product from Amazon and change the address to my eBay customer's address, so it goes to him. Do I have to collect sales tax? I'm in California. I know if the customer is from California I do collect, but what if he is from out-of-state? Should I collect all states that Amazon collect?

Do you know exactly where the client is located? One of the issues you run into is that the Amazon fulfillment program can create tax nexus for you in certain states. It technically means you have tax nexus in states in which you store your inventory in Amazon fulfillment centers. Amazon stores inventory in the following states: AZ, CA, DE, FL, IN, KS, KY, NV, PA, SC, TN, TX,VA, WA. Separately, are you actually paying sales tax though when you purchase on Amazon? It's possible the original seller on Amazon could be subject to FBA and then you would effectively be a re-seller.