That looks like 'Atropurpurea' to me. I'm far from a maple expert though, my interest is mainly conifers.

Dax

'Atropurpurea' should have much darker, redder leaves than that :-)

Without seeing the tree as it moves/changes through the seasons, its growth habit and some perception of mature size, it's difficult to be very specific.....it looks pretty generic :-) I'd suspect it is just a seedling Acer palmatum - no cultivar. Is there any obvious graft?

'Bloodgood' is probably the most highly propagated form of J. maple and not all propagation is done by reputable growers and to the same standards. A great many seedling trees are sold as 'Bloodgood' when the only sure way of propagation is by grafting from known stock (or layering). There is no guarantee a seedling will resemble the parent plant and appearance, both in leaf size and formation, coloring, etc., can be extremely variable. And a seedling JM, regardless of parentage, cannot technically be sold under any cultivar name - it is only an Acer palmatum seedling :-)

But that's not to say these will not develop into perfectly attractive little (or not so little) trees and often with great seasonal color.

There is an obvious graft, the root stock has a green bark to it. So not a seedling but an intentional graft. My wife thinks it is Deshojo but we don't know for sure having never seen that variety before..