One of the problems we have had in the past with many projects is "feature creep". We have been using a fixed bid system with a set number of deliverables which protects us from large losses. After one deliverable, if we don't get paid, we stop working on that project. There is a fine line between what is an acceptable "enhancement request" that is unbillable and one that we would have to bill for.

We don't want to seem to inflexible. We'd like to keep a good working relationship with our clients but at the same time we can't afford to make to many changes to the project because we risk going over budget and cutting into our profit margin.

Are there some client management tips early in the design and development process that can reduce some of that strain in the business relationship? Perhaps there are sme things you could let your client know early on, that would make them understand when you tell them those pieces "they have to have" will be billable.