I would say that it is very, very, very important to have an invoice for every single order you make, whether it’s from a retailer or a wholesaler.
Personally, I started focusing more on wholesale, but I still engage in Online Arbitrage (OA) and buy from retailers that are reseller-friendly and provide invoices.
Make sure that the billing information on the invoice matches, letter for letter, the details on your Amazon account.
Ensure that the invoice clearly shows the name of the product and is easy to read.
Do not buy from third-party sellers, but only from suppliers (retailers and wholesalers).
This is my approach, and I hope others can add some more advice.