To me its always a red flag when a company rep says " nobody backdoors here". Its impossible to know and its rampant across the board. I used to label my bank statements in a discreet way and had my reps who i trusted at these funders be on the lookout for subs that come with my labeled statements so I have "busted" even the most reputable shops ( would customize the bank statemnt label for each sub and actually caused a few reps at certain shops to be relieved of their jobs).. But I no longer waste time being a detective as I saw how widespread it is . Of course when I find out with certainty its happening I limit my subs there unless despite the backdooring I am still converting alot with said funder. But no matter what you do security wise all it takes is one rogue employee to want to make alot of extra side money for the backdorring to happen. My advice is keep your focus on the shops that convert for you and dont just blast out every sub. Limiting the exposure will limit the backdooring.