So you ordered 7 grams of weed and got 8. That's great, really. But whether the vendor was feeling generous, or he wanted to get rid of the last of the bud from that harvest, it was an anomaly. If they were willing to do it for every order, they'd just lower their prices. The vendor did something nice for you, and announcing to everyone in the feedback that you got more than what you ordered is not a good way to repay them. It just leaves customers open for disappointment when they don't get anything other than what they ordered.
I just feel like a vendor giving a you a bit extra is one of those things you keep your mouth shut about, and if you want to repay them, you go back to order from them because finding someone who isn't a greedy fucker can be pretty hard.
Maybe I'm the asshole here, though. Just my thoughts.
You were right at the end of your rant, you are an asshole.
I am not a vendor but I used to deal quite a bit to get through college and it was always my practice to throw an extra bud in with every order. Why? Because sometimes your customers take the order home and throw it on their scale to make sure you didn't fuck them. Throwing an extra gram on the order gives you some leeway for scale accuracy differences. It also saves time having to break buds in half over chump change. The nature of the business is that if someone buys 7 and get 8 they are happy as a clam. But buy 7 and get 6.9 and the customer goes fucking nuclear.
If someone adds it into their review that they were overweight it demonstrates that the vendor is unlikely to short you. If they order 7 grams and get 8 grams of pure shit, the extra gram isn't likely to save the review. Announcing that the vendor errs on the side of the buyer when weighing out the product is absolutely relevant to the review.