So I recently bought an upper and when I took it apart the BCG was unmarked, abnormal staking as well. The upper didn't have any marks that I saw either and the barrel only had caliber and twist printed on it I think.
The seller said it was a colt upper receiver, but I'm not sure at this point. I'm also a bit new to this so any information would greatly help, thanks.

Welcome to the forums.

Unfortunately, that is not a Colt receiver. Colt receivers are marked either with a "C" or their cage code "13629" depending on when it was manufactured. They will also always have a forge mark on them.



If I remember correctly, "D" marked bolts were DPMS. It looks like someone re-staked the gas key afterwards.





Also, when linking pictures, you have to link each individual picture to the thread one at a time. You can't link an Imgur album and have the pictures appear.

Oh ok got it, thanks. Didn't know I had to post separate links

Sorry, didn't know I needed approval to post pics, how should I go about doing that?
and I guess buyers inexperience since it's my first time buying AR parts and also my first AR, also I bought it from a local gun store so I thought they would be pretty credible.
Live and learn I guess, I'll see if I can somehow get that sorted out with the store, any tips that might help me with that?