If I sell something the buyer can do whatever they want with it, if they mark it up an resell it then that's on me because I didn't charge enough. Conversely if you sell me something, I bought it because it has value to me, either because I want to use it or I think the price leaves me room to make money or I think the market will go up and I can make money in the future. If any of that bothers you, don't sell to me.