Considering Buying Uncertified Lab-Grown Diamond Earrings – Convince Me Not To

I was offered a good deal on some lab-grown diamond earrings, but of course the big catch is that they are uncertified. Is the big issue here basically that there is no way to guarantee you are getting what you actually paid for? What if you have a good relationship with the jeweler and trust them? (as much as anyone can trust a jeweler). They will still write an appraisal for insurance purposes, and I'll be able to inspect the diamonds in person before purchasing. I don't care about resale value. Please help me understand the downsides so I can make an informed decision. Thanks