Your mortgage company would care about where you're finding extra income from because they need to know its sustainable. They may not care where you get the deposit from but they won't just take your word for it that you've suddenly found a new income stream that will carry on for the next 25 years. The approval process is just a box ticking exercise though where 777 have to meet certain criteria to pass all the stuff in the background doesn't matter if they tick the boxes they have to tick.I suppose the whole pl approval thing would be something like this...
You ask a mortgage lender to give you money for a house, on the application you show your wage/income, the mortgage company wont approve it because you need to prove you can generate more income. The mortgage company dont give two hoots about rumours your finding the extra money by dealing drugs on the corner of the street?