I'm writing a proposal to do some recurring work for a client. I'll be selling them services, packaged into a unit, and they may need none, or several of these units in any given month.
The question is: how should I charge for these units, given that the amount I'll sell to the client each month is variable?
Ideas I can think of (some better than others):
- simply bill up-front at order time for each unit (or 50%, or etc.), which could result in an invoice per week if things heat up - lots of paperwork
- charge a fixed retainer, then charge the balance at the end of the month (or refund the retainer), which balances risk somewhat and ensures I get at least a little bit of pay no matter what
- bill at the end of the month, assuming all risk myself
What's a common way to handle this pattern? Are there others I haven't thought of?