I dont beleive this is unscrupulous but rather representing your sellers best interest as their listing agent. You have a buyer that is not performing and the deal looks shaky. You call someone that was interested in the property and tell them it looks shaky and if they are interested they have a chance to bump the person ahead of them. They submit a back up (hey they dont call it a back up offer for nuthin’) knowing full well that the person ahead can get their act together or lose the deal. Sometimes it pushes the buyer to perform (a good thing if you are the seller) sometimes it shakes out a weak buyer sooner than later. Nothing unscrupulous there.
As for the mortgage broker, they shouldnt share financial information unless expressly permitted by the buyer client. As for telling what you could “qualify for” thats not a big deal because with todays lax loan underwriting you can qualify for just about anything via stated income loans. Any decent agent knows that and relies on the numbers their buyers tell them they are comfortable with not what they qualify for.