The main loan sharks are banks and financial institutions who dress themselves up in legalities and color brochures
Only knew one "loan shark" tho only met him a few times thru other contacts - but he was a vicious son of a bitch, despite he had plenty assets (at least over $30 mill - that we know of).
His speciality - tho he never got involved personally, was to dump his defaulters down a manhole (not sure it's the same terminology elsewhere - these holes in the road!) and pour gas down the hole and a match after it. Nice guy. These incidents were often news reports and was his method of reminding other borrowers that they owed him money.
He's in his 60's now and last time I saw him, he was in a supermarket toddling along behind his new "mail order bride" - obviously totally devoted and in love
But... he's still a dangerous man and vicious if anyone defaults. Strange character.