so your “guy” is either a idiot or a liar…(can’t rule out “both”).
you can convert CBD to D9 or D8, you can convert D9 to D8, but nobody out there is running D8 back to D9.
I’m not familiar enough with the chemistry to say it can’t be done, and given the number of ways that have been offered up for Carboxylation - Adding the "a" back to THC - #7 by cyclopath, I’m not willing to go out on that limb, but even if folks were making D8 into D9, it would be D9…
folks are certainly selling D8 as D9…and D8 will not get you as high as D9.
I suggest you take up TLC, and use a kit to get you going. Shop | Cannalytics Supply