"Marcus smells greatly of cheese."
Translation:Marcus caseum valde olet.
It's just a weird fact of how the verb works: olēre , to be redolent (of).
Checking the Oxford Latin Dictionary just now, I see that both constructions are possible:
olēre + the accusative: a 'cognate' accusative (as in, "to sing a song," "to make a poem," "to ask a question") = "to give off the smell of";
but also olēre + ablative = "to smell of."
A lot of the time, it's used with an adverb (i.e., it "smells good" or it "smells bad"): bene / male olet.