If the Seller (Owner) has substantial Equity in the Property, then they can carry that for the Buyer:
In the extreme; if the Seller owns the property, outright, then they can do anything they want, a Bank does not have to be involved at all.
If you have such a situation, you can sign a NOTE with the Seller, putting down anything they want, or nothing. You can set any Interest Rate, etc.
Please involve a Realtor to protect your interests.
Good luck and may God bless