I bought a TMM4A1 on Ebay
Without knowing what he had done externally and internally, the best advice I can give, is that airsoft guns generally lose about 1/3 to 1/2 of their value on the used market. This is just a generalization from my observations. Others, more experienced than I, may say otherwise.
There are no externals, but it does come with a battery and charger.
$500 seems a bit of a stretch to me, he must have included the exorbitant shipping rates.
From what I have seen, most TMs m4s customs with MBKS ONLY (no internal upgrades) go for about $380-$400
I shoot Table Gypsies on sight!
I'm sure the high cost is because it's from Redwolf... Shipping/Handling is expensive.
DJ (Dennis)