Here’s a sleazy trick that headhunters use. They say “Tell us where else you interviewed, so we can avoid double-submitting you.”
Superficially, that seems reasonable. What’s the problem?
The headhunter is fishing for leads. You tell the headhunter where else you interviewed. The headhunter finds out who is hiring. Then, the headhunter is going to call them and try to sell them.
There’s an easy workaround. If an interview doesn’t go anywhere, mention it when headhunters ask.