A factual error - here a misdescription - is not a logical mistake, an error in reasoning, an instance of invalid argumentation. It is still only a factual error if there is an intention to deceive.
On this site you will find 'fallacy' confined to logical mistake. There is a different, more popular sense in which a 'fallacy' refers to 'Deception, guile, trickery; a deception; a lie' (Oxford English Dictionary). This is perfectly sound usage and it appears to be the one you need, but (sorry) it isn't the specific usage to which we confine ourselves here.
The following interesting comment has been made :
May be the premise that is presented is not a logical fallacy to the strict usage of the term in terms of logical reasoning. But if one needs to attack the premise, won't the person use some logical method? Would that be formalized in the terms you use here?
Just a minor point : it's the argument that's fallacious rather than any particular premise that occurs in it.
But of course, you are right. The misdesription would usually, and always could, be attacked by means of argument. Here's an example :
1 You advertised X as a cheap car.
2 X is cheap but it does not have the functionality expected of a car under
the usual understanding and trade description of what a car is.
3 Therefore you have given a false description, relative to the usual understanding and trade description of a 'car', in calling X a car.
4 Therefore you have given a false description of X.
5 Since fair trading requires accurate, not false, descriptions, and your description of X is false, you have traded unfairly.
This argument could be tightened up but I think it indicates the line of attack you have in mind. Hope this helps.