malpractice? cars are registered and updated every day, legally, without having the title transferred to the buyer's name.
If you are PAID for advice and offer advice which could, indeed, is illegal and can cost your clients their ENTIRE investment, yes, malpractice.
"Registering" a car (marbete) and "titling" a car (matricula) are completely different legal animals.
If you suggest to a client that they can buy & sell a car without the title ever being in their name, you are indeed guilty of "malpractice."
Why not just offer legitimate, legally-sound and law-based advice? Heck, why not educate your clients in the law? Why would that present problems?
Certainly you can run your legally unregistered, uninsured and untaxed business anyway you want. And no doubt some, who don't understand or care about prevailing law or legal legitimacy, will ask for assistance. Great! Certainly under-the-radar businesses can operate less expensively and that is attractive to many either by intent or ignorance.
I'm just surprised your first question isn't "is there a clean, legitimate title" like when you buy a car in the states or Europe. It all starts from there.