Can my landlord refuse my buyer because it would violate an exclusivity deal with another tenant?

Yes, generally this is a legitimate reason for a landlord to refuse or condition consent. If another tenant in the same plaza or building has an exclusivity clause in their own lease preventing the landlord from leasing to a competing type of business, and your buyer's intended use would breach that commitment, the landlord has a real contractual obligation to another party that consent to your assignment could put them in breach of. This is treated as a legitimate, business-driven concern rather than an arbitrary objection.

This risk depends heavily on what your buyer actually plans to do with the space versus what your business does now — a straightforward assignment where the buyer continues the identical business is far less likely to raise this issue than a sale where the buyer intends a different or expanded use that edges into a competitor's protected territory.

Because this kind of conflict can only be assessed by looking at other tenants' lease terms, which you may not have visibility into, ask the landlord directly whether any exclusivity commitments could affect your buyer's plans. A Treadstone business lawyer can help assess and address this before it derails your sale.