Lenders do not receive a commision nor are the bonuses based on mortgage production.
Even though no commissions or bonuses, many banks have some type of performance goals or minimum quotas for loan officers. (If not, LO's would not be hustling the way they usually do.) The incentive would be to keep employed by the bank.
Some banks do have LO's approving other LO's loans. I personally think it is a bad deal, because again, "you scratch my back, I'll scratch yours." IMHO, I would still disagree to LO's underwriting their own or another LO's mortgage loans.
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Integrity. With it, nothing else matters. Without it, nothing else matters.