LSD tartrate isn't stable unless kept cool, dry and out of light.
If you want to test if it's REALLY pure LSD, put it in a glass vial (and put lid on), turn out all the lights, shake the vial. If it twinkles - it's legit.
Not hippy BS, LSD is triboluminescent and I have seen it because before his bust, Casey sent me a gift. I kept telling him 'make an analogue, they are LEGAL' but he just kept saying how he wanted to prove a point. Yes, and he spent 13 years and 8 months MAKING that point.
Pure DMT also demonstrated triboluminescence but I haven't seen it since when I got my gift, I didn't know the trick.
Maybe ask the vendor to film them shaking a vial of it. They may think it odd but I bet they won't know WHAT to expect and it's very distinctive and sparkly. It's white light but ask what COLOUR because then they might try to guess but all pedants know white isn't a colour, it's a shade.