Is your Marlin an older Pre Remington model ? If so it's priceless.
Put it this way. The 770 is like a $400 Canadian Tire Special. And it's only $400 cause CDNT is a bit overpriced. At least ours is.
A Tasco scope is also a Canadian Tire special. Worth like $150 max.
Used, his whole rifle is only worth like $400.
A Pre-Remi Marlin 30-30 is like $700-800 if you find one new. Used maybe about $500 WITHOUT a scope as per my local prices.
You could trade for a much better rifle if you really don't want it. Our local used dealer won't even take a 770. You should be able to trade it for at least a real 700 or a decent Savage from a reputable dealer, and just keep your scope for whatever you trade it for.
Even if you did trade for his 770, Again keep your leupold, to put on the 770, trade your rifle for his rifle, and he still owes you like $200. And make sure you hit your moose first shot in case the gun jams during the followup.
A Pre-Remi Marlin is like a steak made from an exotic meat that is no longer available cause the animal is endangered. A 770 is like a 1.39 special from McDonalds.