What you are doing is known as a "drop shipment" in the state and local tax world. Each state has it's own drop shipment rules. The answer is way to complicated for a free online service like this and I do recommend you get an accountant or lawyer with knowledge in drop shipments to make sure you are complying with the laws of the states in which you sell.
If you'd like to do a little research own your own first, then search for "drop shipment sales tax listing by state." Also look for web site for the streamlined sales tax project, which has listing of rules for some of the states. The multistate tax commission may also have download that can generally help.
Just remember, if a state proves that you should have been collecting tax and you did not, then the state will hold your business liable for the tax for as far back as the statute of limitations in that state will allow. This is one of those things that are work getting right in the beginning.
I hope this helps.
Generally, you have to collect sales tax for any state where you have a physical presence, and it is based on the place of delivery. This is not a completely simple concept as state taxes never are. I can almost guarantee you will be collecting sales tax for sales in NY to the extent that they are imposed by that state.
If you are physically in New York you should collect on NY sales. There may be an issue as to whether you also have a presence in Florida where the fish are. You should check with an accountant.
....how do you sell fish online? I mean do they ride in coach? sorry, it just sounds funny and the internet is changing so much.
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