I also see a problem with the opening and closing of the different channels for each shop you buy at
It's much cheaper just to leave it open as long as possible (channels can be left open permanently)
this would incentivize opening a channel on a big merchant and always buy there (say amazon starts accepting LN payments, then most people would go there always and not give a chance to the smaller merchants just to save the money from opening a channel on other online shops). This would make it even worse for them.
You don't need a Lightning channel for every person or store you send to. Money can be routed across multiple channels, so as long as the overall network is well connected, there's not much advantage to who you open a channel with. It's probably better to open channels with more neutral intermediate channel operators, they'll almost certainly try to gain some advantage from opening channels directly with big businesses (that's not going to be an easy business to be in when the barrier to entry is so low)