I have my GED and agree with @MrItty.
I must say though, I have no clue where my paperwork is. But, to obtain it you actually have to contact your state. For me, I’d have to contact Harrisburg (PA) to get a copy of the results. I took the exam at my local community college, but they do not keep the records like that. I had to get the results then take them to the school when I applied to it.
Also, I’ve never had anyone doubt me. Do they have no college completed at all? You cannot go to college without finishing high school/GED, so I guess that’s proof enough to most people in my case.