Does a non-solicitation clause stop a seller from contacting old customers, or only old staff?

It depends entirely on which non-solicitation covenant is actually in the agreement, since employee non-solicitation and customer non-solicitation are legally distinct types of clauses that a purchase agreement may include one, both, or neither of. A clause limited to employees generally only restricts the seller from soliciting or hiring away people who work for the business, and would not, by itself, say anything about the seller contacting former customers.

Many business purchase agreements do include a separate customer non-solicitation provision precisely because customer relationships are often central to the goodwill the buyer is paying for, restricting the seller from soliciting the business's customers, clients, or accounts for a defined period after closing. Where an agreement includes only an employee-focused clause and no customer-focused one, a seller reaching out to former customers may not breach that specific covenant, though it could still raise separate concerns under a non-compete if the seller is using those customer contacts to compete more broadly. Reading the actual defined scope of each clause, rather than assuming "non-solicit" covers everything, is the key step.