wait, wouldn't this cause buyer's remorse? like, if I just finally decided to buy some product ... being bombarded with all the other options suddenly makes me rethink my purchase decision, "oh but what if this other one is more gooder!?!?!"

I think the argument is cognitive dissonance and confirmation bias generally function to make you more happy with the one you bought already when presented with other alternatives.

I thought that cognitive dissonance was the buyer's remorse. I've experienced that a few times in my life. Now I've got no qualms about immediately taking stuff back.

Exactly my thoughts, you might see there something with better/more reviews.

What are the (general) financial consequences of buyer's remorse?

For Amazon with a generous return policy, when a person has buyer's remorse, they can return the item. Lost sale.