Even the 1Ds2 has the 5D3 beat when you're at ISO 100-200 with very good (read: clear & plentiful) light. The 5D series does do better than the 1Ds line when you step into those higher ISOs—there's a reason why ISO3200 was only ever a boost option on them—and I think if you are going for low key with a lot of shadow detail then the 5D line just about wins, but when you're talking about moderate or high-key, low ISO images, Canon did something to those 1Ds cameras that made them over-deliver. Give them studio lighting on full blast and you're not going to find anything better within the Canon world. Skin tones, especially, have not been bested since the 1Ds2. If you shoot studio portraits and you've never shot a camera with the DIGIC II processor, you're missing out.
In this particular case, it does seem like the deal is a touch too good to be true. The 1Ds cameras are built very solidly, but even the toughest cameras can be broken or wear down. A pro body like that has, most likely, seen a lot of use, and while it's uncommon to see one with the shutter run all the way down or haze in the viewfinder or a coughing mirror or anything like that, it's not totally out of the realm of possiblity. It's also very common for the batteries for the Ds cameras to have been completely worn through, and new batteries cost a helluva lot. The Ds line has definitely lost value quickly over the last year but if it was in good condition it'd still be worth a fair bit. Worth looking into, but not worth taking a blind chance on.
