I found the account of someone I used to know by recognising a random picture she posted as being the same as had been on her instagram before she deleted it a while before. The chances were incredibly slim of it happening as there was zero identifying information in the picture, just that I had seen it before and it had stuck in my memory. Her instagram wasn't easy to find either.
She had always acted like she was right about everything and everyone was beneath her. I read her posts and found she often tried to shill her partner's business, pretending it wasn't connected to her. I waited until she did it again and pointed this out publicly. She denied it of course, replying in a really patronising way, pointing out a minor unrelated mistake I had made in my post as a way to discredit me. That just made it more glorious.
I then posted overwhelming proof. She deleted her posting history, the page I linked to on her website, and had my post removed. She then tried to continue using the same account so I replied to her again asking why she had denied it yet deleted things and what a coincidence it was that the website had changed too. She stopped using it after that and deleted her posts again.
I'm sure she's posting on another account now as she posted something and then quickly deleted it (I set up a service to get emails when she posted for a bit). The great thing is that my post detailing what she did still shows up when her name is googled as it's still on my profile and her name is unique.