It depends on the service that you are performing and the budget of the campaign. In my agency, we typically stick to monthly minimums, so we know we are getting a least a certain amount per month from each client. In general we might do a 20-25% of the monthly advertising budget as our management fee, as long as the fee is at least $1500/month. The only exception is if the company has a small budget, so we may structure our fee on a sliding scale to sore of help them out while they are smaller and growing, then grow the fee over time as the marketing campaigns grow. On the other side, if the client has a large budget, say 100k and higher, we may have a cap on a the amount we are charging per month, somewhere in the $5k to $10k range depending on how much management work is involved in the management engagement. I hope this helps.