Even if things had worked out as this person planned, it seems like the bank might have wanted to know where $300,000 suddenly came from, and I don't know how "I took out a sketchy loan against my Bitcoin holdings, which you already don't think can qualify me for a mortgage" would have shaken out.
Someone tries to take out a loan against their Bitcoin holdings to get a mortgage, loses over $300,000
A prospective house-buyer wanted to pad their bank account to try to convince their bank to approve them for a mortgage. Their bank didn't consider Bitcoin holdings when evaluating a person's suitability for a mortgage (can't imagine why), and so the person decided to take out a loan on the BlockFi platform, putting up $600,000 worth of Bitcoin as collateral for a $300,000 loan. However, the borrower had bought their Bitcoin from a private source (rather than through one of the major exchanges), and it turned out the Bitcoin had previously come through a cryptocurrency mixer. Because of what BlockFi described to the borrower as "indirect mixing exposure", BlockFi called back the loan and the borrower "lost more than half of [their] BTC holdings, have a huge tax bill, and was screwed out of a fortune".
- "Blockfi Horrible Loan Experience (FORTUNE Lost)" on r/CryptoCurrency