Yes, you can limit roommates...to some degree.As I explained above, you should have justification for it.

Canceling the contract without proper justification (those reasons should be spelled out in the contract) will get you sued for "specific performance" and/or "fraud in the inducement" and the seller may well look for consequential damages.Proper justification for canceling the contract is normally limited to home inspection and mortgage approval. 

However, if they wanted to justify it, I'm sure the justification is that renters cause more problems than owners; renters tend to live then shorter periods of time and there are expenses when someone moves in/out such as extra trash pick-ups, programming them into an entry system, cleaning costs as the move in/out can be messy around the building, light damage to the building, scheduling of the freight elevator, cost of providing additional notices as now the tenant and owner need to receive copies, etc.

Do not try to lowball someone with the tax assessed value as justification because unless they are inexperienced they will not go for it because in most cases it isn't the most accurate value assessment.

I understand that the FoxConn project is putting upward pressure on prices, but I don't see a rational justification for a $20K jump in 9 months.

Then if you want to slough the numbers with a justification of how house hacking reduces your monthly mortgage/rent, at least you're armed with the analysis for both scenarios, and can make a qualified decision.Roughly, $500k purchase with $4000 monthly gross rents doesn't hit the 1% rule of monthly gross rents being 1% of the purchase price.

Then you need to make your justification for what comps are most accurate for your property.

If the appraiser deviated from public record without justification or explanation in the report then they are in the wrong.

Being able to make more money from the property and financial justification is typically not considered a hardship.Could you put the property under contract contingent on going to ZBA and getting the other units approved?

If you are set on renting this unit, bring a copy of this to the office and demand justification for your rejection.