Some domain companies will buy the domains you searched and try to resell them for a premium. Happened to me just a few months ago. I was using a GoDaddy search since it seemed like a useful way to bulk search some tlds for what I wanted. Looked up a few things that I'm almost 100% sure nobody else was looking for since they were very unique. Didn't buy them that day, but spent a while browsing them using the GoDaddy search tools.

One day later I decided I was ready and went to buy one, but everything I had searched was suddenly only available to buy jacked up with a huge "premium" fee and seemed to be owned by GoDaddy. Never again will I search using their console.