I've had clients I've worked with who I'm pretty sure are not going to cheat by skipping paying.
Two options in cases of doubt is to put money up front in escrow, which nearly eliminates non-payment risk.
How will I know whether I should stick with principle of asking for partial payment upfront, when working with existing clients, or simply getting paid at the end?
Preface: I don't work with crowd sourcing sites such as elance, odesk or similar. I work with direct contact clients and not through some middleman portal. For this reason I have direct contact information with the client, their accounting, etc as they do mine.
I always charge a percentage up front of any new client which I've never worked with before - regardless of how we came in contact with each other.
However, I never charge a deposit or percentage up front for a client I've worked with (successfully) in the past. Previous clients have already proven the ability and willingness to pay. I've never been shorted by a previous client.
The initial, first, project with a client is an exploratory phase for both you and the client. You're protecting yourself by requiring an upfront fee. The client is protecting themselves by not paying everything up front. Once business trust is established - you know they will pay and they know you can complete the work - that extra level of protection is often not needed in my experience.
Always ask for a percentage upfront for any new client. It's a good practice.
What about the existing trustworthy clients? Don't become to bureaucratic with them. Because you are a freelancer, what they really need for you is to bear as much risk as possible and first of all to get the job done without wasting too much of their time (I'm speaking about repeating customers who you do know for a fact that they will always pay their debts). What you should never do is price reductions, too many concessions just because they are coming back to you with more work need to be done or low prices just because you are a freelancer.
If you mistrust a repeat customer, why are you continuing to accept work from them?
I agree that you can ask for payment upfront; that will 1.)scare away any potential scammers 2.)show you're serious about the job.
