In Petrosky v. Zoning Hearing Board of the Township of Upper Chichester, 485 Pa. 501, 402 A.2d 1385 (1979), the Supreme Court held that, in determining whether the holder of an erroneously-issued permit has a vested right in a permit, a court should consider: the permit holder's due diligence in attempting to comply with the law; his good faith throughout the proceedings; the expenditure of substantial unrecoverable funds; the expiration without appeal of the period during which an appeal could have been taken from the issuance of the permit; 5. the insufficiency of the evidence to prove that individual property rights or the public health, safety or welfare would be adversely affected by the use of the permit. Id. at 507, 402 A.2d at 1388.