Do the thing, step by step.

Pick one category you can source repeatedly, register the business and get an EIN, set up resale documentation and a business bank account, buy a small first lot, and record every cost so you know what you actually made.

Buy on prepayment first, build a short record with that supplier, then apply with an entity, an EIN, business bank references and two or three trade references who will confirm you pay on time.

Price the load from the manifest using your own expected sell prices and sell-through rate, add freight and refurbishment, divide by sellable units to get landed cost, and only bid if that leaves your margin with room to be wrong.

Start from landed cost, set a target margin by category and grade, check it against what the item actually sells for locally, and build in an automatic markdown schedule by age.