The items you are currently selling need a business account - that is a requirement rather than a choice.
If you have personal, pre-owned items that you would like to sell on Ebay, you can open a second account for those items.
You can't trade on a private account, selling new items you have bought to sell.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)