I traded $625 worth of my custom knives that I make for my like new, JM stamped Marlin 444 in similar condition. Mine does have the crossbolt safety but was without the box. The seller and I both felt it was a fair trade both ways. I’d imagine the one your looking at would be worth $600-750 TO ME, depending on how much you value the box and accessories.
I’d feel a little guilty walking away with less than $600 and personally at $750 your out of my price range given that Marlins are not really all that uncommon even in oddball calibers. I also don’t anticipate it ever being worth a fortune over what your going to pay for it now within your lifetime, JM stamp or not so as far as I’m concerned it’s an investment that will HOLD value but not really GROW as compared to other options after accounting for inflation over time. At over $750 I’d be looking for another clean user personally.