Re: So how long before ...
"The selling price of the first thing I bought is not affected buy the buying price of the second."
Please tell me you didn't vote..
In your home it might work like that.
In a business the selling price is directly related to the cost of replenishing the stock.
In fact, the value of the stock is directly related to the market value of the product, so why would you sell it at a lower price?