> If there is money involved, I will have to scrutinize the CVs and pick the strongest ones.

Yes. Employment law tends to require that.

> I would say I'm doing a fairly generous thing already by sharing my time

Things said by every person who has ever offered an unpaid internship.

> I did meet students whose primary care is the payment (usually because of family factors)

Everyone has a right to be paid for their labour regardless of their circumstances. As an employer you wouldn't even get to ask them why they needed the money you were going to pay them. This is a layer of protection for employees enshrined in employment law. Everyone is entitled to privacy in their personal lives.

> I cannot offer that.

Then don't. But also with respect, don't find a loophole around it either. It is categorically the wrong thing to do.

It is entirely possible for a person to have good intentions and then do the wrong thing.