How many times have you had a client make so many revisions that you forgot what the original idea was? How many times were you paid appropriately for all of those revisions? All to often, the math doesn't work out in favor ot the freelancer. Which is exactly why you need to start thinking about this.
Look, I will freely admit that after two decades of doing this, I still manage to screw myself out of some significant coin because I don't set the proper parameters up front. There is simply no way to accurately forecast how much conceptual and production time it will take to meet a specific creative expectation. So how the hell do you and the client create a realistic, mutually beneficial budget?
Let me present two helpful items:
"Not to Exceed" —
The only real protection you have in your relationship with the customer is your contractual understanding. This is where newbies get it wrong most of the time because they simply don't have the frame of reference. Listing services as line items in your contract provides a couple of benefits. One, it gives the client an understanding of why the total equals what it does.* Two, it protects you from grossly mismanaged relationships where the client will take advantage of revision time if it is not protected.
Therefore, if you believe the PRODUCT will take 40 hours, it is in your best interest to protect that with an addendum stating that this particular item is not to exceed six additional hours, or two revisions at X hours per revision. If this time is exceeded, a change order will be issued prior to completion of the product.
*The danger in listing all of your services à la carte is it also gives the client an opportunity to delete services they think are relevant to the overall campaign, even if you know them not to be. So take into account that essential items should be "buried" within the cost and not given an opportunity for edit.
"Blended Rates" —
There are pros and cons to listing all of your labor rates within a contract. What often happens is this becomes a point of irritation to the client based on their varying understanding of the complexities of those labor rates. Therefore, create a blended rate of "X" dollars per hour for a group of tasks. For example, you might want to classify conceptualization, copywriting, and scripting as a blended rate of $100 per hour. Graphic design, web design, and logo development is at a blended rate of $150 per hour. Etc. This allows you to protect like-minded services within a grouping and minimize confusion as to what the client is paying for.
Take into account these two critical keys in your contract, and you should adequately protect yourself from losing too much money based on scope creep.
If you have any additional tactics or techniques that you utilize for scope creep, this community of marketing warriors would love to benefit from your knowledge. Please drop it at will.