What type of arrangements are illegal according to anti-trust law?

Tying arrangements are considered illegal under antitrust laws because they restrict competition and can create unfair market dynamics. A tying arrangement occurs when a seller requires a buyer to purchase a secondary product or service as a condition of obtaining a desired primary product or service. This can limit the choices available to consumers and can force them into purchasing additional products that they may not want or need, thereby stifling competition and innovation in the marketplace.

In contrast, commission divisions among agents may be permissible as long as they are disclosed and comply with regulatory guidelines. Exclusive listing agreements are also legal as they provide protection for real estate professionals in exchange for certain obligations from the seller. Tenant agreements generally do not fall under antitrust scrutiny unless they engage in practices that restrain trade, which is not typically the case. Thus, tying arrangements are singled out as illegal due to their clear potential to harm competition.