"You do not like the new merchant."
Translation:Mercator novus vobis non placet.
Vōbīs is the only way of getting "you" into the sentence: it's dative case, because the verb placēre "to be pleasing to" requires a dative object.
Grammatically, in Latin, "the new merchant" is the subject of the verb, in the nominative case; literally we could translate: "The new merchant is pleasing to you" (where YOU is plural).
I had one denied because of word-order as well. I had written, Vobis mercator novus non placet.
I wonder how free the word order of standard spoken Latin really was. German has time-manner-place rules which sound odd to English speakers if translated literally. Was Latin really used so flexibly? I'll google and see what that turns up.