Here the Kitzur SA prohibits getting involved in a business transaction that might depress the price for a fellow Jew...
The following is based upon a true story:
Once upon a time, Ari the Mashgiach was learning at his post, which at that time was perfectly OK with the boss. Then in walked a Jewish man "Abie" and teased Ari to his boss....
Abie: "He's strong and he can work. He doesn't need to just sit there idly"
Ari was upset and afraid that his relationship with his boss was being undermined
Ari cried to Abie: "Parnassah! You're hurting my parnassah!"
B"H we have a happy ending. The man Abie was quite learned and quickly realized his error and apologized. He performed the requisite "Piyyus" as outlined by KSA here.
Otherwise, Ari's physical workload might have been increased, w/o a corresponding increase in pay and either his learning time would have decreased. Or
he might have had to find either a better paying job to make time for his lost Torah time