For me I can accept that the dealer has to install "something" to make the vehicle flat towable.
But I would not accept a condition like "disconnect the negative battery terminal". Since a flat towable vehicle cannot be backed up it's enough should a quick disconnect need arise without having to open the hood, find a wrench and reconnect the battery cable.
BTW My JGC battery is under the passenger seat and access is much more involved than any other vehicle I've owned.
OP With a pending purchase do your research and understand every aspect of towing requirements. There are thouslands of posts of folks wanting to tow existing vehicles and then the "surprise" game unfolds.