Can my landlord use the sale as an excuse to raise the rent before agreeing to anything?

It depends on what your lease actually authorizes the landlord to require as a condition of consent. Some leases give the landlord fairly broad discretion over the terms of an assignment, which can be read to include renegotiating rent; others limit the landlord's role to assessing the proposed assignee's suitability — financial strength, business experience, intended use — without opening the door to unrelated demands like a rent increase.

Where a lease includes a "not unreasonably withheld" standard for consent, using the assignment request as leverage to extract a rent increase unconnected to any legitimate concern about the assignee can look like an improper condition, though this is fact-specific and depends on the exact clause and circumstances. A landlord is on stronger ground if the rent increase is tied to a genuine renewal or extension being negotiated at the same time, rather than simply as a price for approving the buyer.

Because this is one of the more contested areas of lease assignment practice, it's worth having your lease's consent clause reviewed before you respond to a rent demand. A Treadstone business lawyer can assess whether the demand is tied to a legitimate condition or is really just leverage.