Just an idea: short your merchandise. (pre-sales)

Here’s the idea: you have little money to create an inventory and to incur in marketing and vending costs. So what you do is, you find a reliable source for those parts, calculate how much you want to profit (counting in sales and marketing expenses) and go around selling your product (online or door to door) without having the inventory ready. When you sell an order, buy it from your source and deliver it to your client.

Risks: very large orders that your source can’t deliver. Make sure to ahve some back-up then.