USAM has a "Payment Method" line item on their posted sales listings. It is the seller's choice how they want to receive their payment. If a cashier's check was the payment method requested by the seller, then you are welcome to ask whether they will accept another method, but you shouldn't be surprised if they say "no." If the seller had other payment methods listed in their ad, but will now only take a cashier's check, then you have a different problem.
When purchasing a used item from an unknown seller there is no way to receive the "protections" you receive when you purchase from an authorized dealer. When buying used, you are incurring higher risk for the benefit of paying a lower price. If you cannot accept the risk, then purchase from a dealer.
Buying used speakers carries more risk than buying other gear used IMO, because the condition of speakers is more likely to be disputed due to small dings etc. that may be a big deal to some but not to others, and also because of their sensitivity to shipping damage. Without the assurances that come with positive feedback, your perceived risk increases with respect to how the seller would handle issues such as insurance coverage, a return related to shipping damage, or other potential conflicts that go along with buying used gear. The risk is less for the seller since they already have your money.
Audiogon's long-time feedback process and documentation can provide greater perceived protection (that you are dealing with a trustworthy individual), and IMO (regardless of what some say) PayPal does offer some protection from fraud and goods that are not as-advertised - not perfect but better than a cashier's check.
