RebelBroker has a nice idea but here on Long Island, our Board has declared that all it takes is to have a note hand written from the homeowner (which again you can't really verify the hand writing unless something goes really wrong and you end up in court or something) stating that they want all offers going through the LA and that's it... You can get this letter at anytime so most agents get something signed as part of their listing package and you (as a selling or buyers agent) will never have a shot at contacting the homeowner and if you do, you're in a load of trouble...
Dan Ortiz ABR CRS CREOS (Hablo Espanol)
Licensed Broker/Owner
Manor Gate Real Estate of NY Inc
"If you think hiring a professional is expensive, wait till you hire an amateur" Red Adair