It certainly looks like one to me! Although unimpressive and a damaged image, this is likely another similar to some of the "finds" I've made because dealers who are generally interested in turning as quick a profit from "junk" as possible don't usually bother to try and find out anything that isn't obvious. Some of my unlikely finds, all of which I've featured previously:
Like you, I can't say with certainty that this small tintype is a soldier; however like yours, the brass buttons on what appears to be a shell jacket are a pretty good indicator!
The dealer I bought this one from for $20 should've known better - I've known him for years and he certainly looks for military items, but the dark image probably didn't look like it was anything. Once out of the half-case, however, the Union forage cap he's holding becomes much more obvious:
The above was found in a box of $2 CDV's, most of which like this one had backmarks from someplace called Manitowoc, plus the faint pencil inscription above the portrait. With only a little digging, here's the result: https://civilwartalk.com/threads/pvt-louis-b-lacount-co-a-5th-wisconsin-vol-inf.138371/ Of course the last fellow who I purchased from a box of junk photographs is one I have featured many times, the latest only last week. From his backdrop it appears he's a North Carolina Confederate officer:
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There is a large auction house/warehouse just north of Culpeper, VA that I visit a few times each year. It resides next to a small motorcycle shop that services my Harley. While my bike is being worked on, I spend a couple of hours carefully sifting thru boxes filled with old family photographs and prints.
Have yet to discover anything ACW related, but it's interesting none the less. You get a close up and very personal look into how various people spent their entire existence working nearby farms. A simpler life that oftentimes reveals the central role that religion played in the community.