Mercury Retrograde can indeed be sticky when it comes to contracts, and I can totally relate to not being able to shut down my solo practice for a month while Mercury mischief is afoot. Here's what I do:
1. Expect misunderstandings, snafus, and for the unexpected resistances and re-negotiations to happen and to try to forestall them by being ultra transparent in advance.
2. Laugh off miscommunications, and quickly take responsibility even when it isn't your fault. This is a form of going with the flow of the retrograde.
3. Have alternative options available in your mind that you can propose that are nearly as good for you / your buyers or sellers and for the objecting party as your original terms. Being more than willing to compromise and give in a little is great for reputation PR and cultivation of trust.
4. Keep yourself in a problem solving / win-win frame of mind -- always good as a business person, but especially during difficult transits like Merc Rx.
5. Be unusually available / responsive to your clients and colleagues, without breaching boundaries, of course.
6. Active listening skills are really useful during this time. And frame your paraphrasing back (prior to addressing points thrown at you) with including your concern or understanding of the emotionality of what you've heard and how much you want to help solve the issue.
In short, Mercury Retrograde is an excellent time for those of us who do project work or are always dealing with contracts to hone our excellent communication and empathetic skills further.