Of course, it’s often a scam. But application fees can be legit. The key is how they are administered.
The fee should not be non refundable, just not refunded under certain specific circumstances.
It’s not fraud if you tell the applicant what the rental criteria are and what happens to the money if they are turned down.
In ancient times, I was a small time landlord. On a couple of occasions I asked for an application fee. I followed these rules, which I explained to the applicant:
It costs money to do background checks. I wasn’t going to be out of pocket if an applicant was dishonest with me.
Not a problem for me. All the software I need is either available as native Linux or runs ok under Wine.
I’m ready to ditch Windows entirely at this point. I just need to find the best way to do that, without having to rebuild the Linux side of my dual boot PC.