Do I have to pay any taxes when I resell for the same price that I bought with

All you are is an agent making a purchase for your principal. You are not going to the store for you, you are going to the store for him. and you just advance the money which he pays you back. As long as your friend pays his sales or use tax I do not see you as owing any taxes. I would like to know how he is "making you buy items for him?" Are you under duress? If you are you need to seek protection.

This sounds like you are acting as either a wholesaler or an agent. As a wholesaler you will need a reseller permit. If you are marking up the goods before transferring. As an agent, the commission is your taxable income and and you will effectively be either a buyer's agent or seller's agent. Or, alternatively, you can be employed as a buyer by your friend. There's several options you have. But since you asked about the percentage, I assume you are planning on trying to make money for this service. As soon as you start earning money from these transactions you will be liable for taxes. You have to make sure to report - probably on a quarterly basis if you are going to be a separate entity. But you have a lot of options and you should decide what works best for you under these circumstances and any changes you make to the arrangement.

This is a strange arrangement. If your friend is somehow avoiding his/her tax liability and you are helping him, there may be consequences for both of you. Perhaps, you should address your concerns in a one-on-one consultation with a tax attorney in your area.