Where a requirement or condition which is not apparently in contravention of this Division has the effect of giving preference to a person on the grounds set out in section 267(2) in a situation where such preference would be unlawful under this Division, the imposition of that condition or requirement shall be unlawful unless the person imposing it establishes good reason for its imposition and shows that its imposition is not a subterfuge to avoid complying with this Division.