Should fundraising firms seek consulting fee in advance from start-ups?

I am mot finance professional and cannot advise you about any financial consequences, yet operational wise I believe yes.

I think yes even at least down payment.

Yes.

Absolutely. Fundraising is a skill and must be renumerated.

Yes, the engagement letter should specify to pay up front consulting fees of25-50 percent in advance and balance as project progress and should also ask for commission on the total amount raised