It can put you at serious financial risk and it's just not worth it. A negotiation is more than just dollars, deadlines, and deliverables. It's also about how the work gets done, who does what, when, and how. If you have particular work methods, you need to spell them out in advance. You will look over this outline and make notes, then get back to me in writing within five working days.
Deadlines are important.
If someone misses theirs, it needs to be clear that the time is added to your schedule. It's also important to spell out how much work is really to be done. Say how many drafts, comps, versions, and revisions are included. If you are doing the work, you must include corrections at any time. But changes are another matter, if someone changes or adds something late in the process, it will cost them, not you, time and money.