Ask HN: Consultants of HN, what criteria you use to charge your clients?

I’m curious to know from other consultants or who do consultantation works here in HN, how do you charge your clients, and I don’t mean the payment method but rather the approach you use:

do you charge per hour, per scope, contract, or something else?

What factors you use to price your services/work?

Do you have a separate contract for each work? Or per client?

Do you have specific payments contract installments?

What tools/SaaS you mostly use? Either in comms, follow up, contract writing and approval, documentation management, payments too or any other tips.

I personally do engineering consulting and refuse to charge per hour, I think clients who ask that they are trying to underpay you, especially if you have a proven record of your outcomes, as per hour rate doesn’t count the efforts you put and have been put outside of these hours, so I charge per scope, I do my initial estimates and based on that I name my price for the whole scope, but curious how others do it.