if you are melting your mouthpiece you're doing it wrong. if you are burning your leg you're either too stoned (which would explain the over-heated core!), or you are just plain ******.
And what makes it particularly galling for some folk is that he (OF) generally is always RIGHT! lol
When in the company of a docent it is a better strategy to ask questions and learn, rather than argue and sulk...
Pre-judging is usually a skill determined by experience, but for a newby smell might be the best clue. If it smells good, it generally is good. Appearance can also indicate quality - clarity and translucence are desirable traits. If it looks "sick", take a pass.
Once you own it, effect and...
I've left oils out in parchment folds for months at a time (forgotten) and have noticed that the original floral flavors dull within a month or two and are replaced by more traditional hashy flavors. Effects become more muted or dulled and the spark is lost. Casual precautions don't seem to be...
considering it as a "food product" and comparing it to something like olive oil you would look to end of life issues like off-flavors and rancidity. those are generally caused or accelerated by light and moisture exposure. cooling is great, just have to keep it sealed air-tight or condensation...
if you don't trust your source, don't buy concentrates! on the other hand, a little butane isn't going to hurt you and the sparking is probably just excess moisture.