(1) the non-compete clause must be reasonable as between the parties themselves. This means the restriction has to be a kind that is no more restrictive than what is necessary to achieve what its legitimate purpose is (which is in the case of the sale for a business to protect the good will that the purchaser has paid for by preventing the seller from setting up across the street and taking all of the clients).
SO ~ look at geographical restrictions and temporal restrictions (time restrictions) + also look at scope / nature of persons property being protected by non-compete clause (must be specific – cant just be this all-encompassing and indefinite vague claim of protecting interests