A Practical Guide to Lawyering Skills by Fiona Boyle, et al.
This "style guide" for Law is in the vein of the ElementsOfStyle, as Boyle et al. prescribe many things which lawyers should do, while mostly failing to explain exactly the benefits and costs of any particular choice.
The best sections cover language use, with such gems as why in legalese we say "good and sufficient", or "Last Will and Testament":
Some of the terms which lawyers reach for have their origins in historical legal distinctions; some reflect the dual use of legal French and legal English five or six hundred years ago.
Shall is a word that is worthy of particular attention. It has been used a lot by lawyers in the past, but is not commonly used in ordinary speech. This means that most people aren't sure of its exact meaning...
So, if you mean, at some future point, the seller can give notice, use "may". If you mean that it is imperative that the seller does give notice, use "must".
Conventions relating to time
From the date of ... the date of the act is excluded Within N days of ... the date of the act is excluded N days after ... the date of the act is excluded Between X and X both X and Y are excluded Until X X could be either excluded or included Beginning on X X is included Commencing on X X is included By the X X is included
This is the sort of language up with which I will not put.