and this is NOT shared by many people, is that you should
never accept a "trust me" from anyone.
Nor should you EVER dive beyond your PERSONAL comfort level and limits. Ever. That's how people get hurt - or killed.
Its
your butt down there. If you screw up at 100', the consequences of doing so are vastly more serious than doing so at 20'. From 20' you can easily swim to the surface. At 100' you might make it - on a good day. If you don't....
With that said, I was certified in a part of the country where the "usual stuff" is in the 80-100' range. My first dive after certification was to 70'. By the time I got five more under my belt I was pushing the triple-digit barrier. But I was trained where dives are done from a boat (and frequently with some wave action to make it "more fun" on the surface), they're "serious" in terms of their depth (no 20' sightseeing missions around here) and visability is highly variable - anything from 60'+ down to 10'-. Water temps range from the mid 80s in the summer to mid 50s in the winter (like now; my last immersion, last weekend, had water temps in the low 60s and out came the drysuit!)
Most of my dives are right around the 100' mark, plus or minus 20. Its just the nature of the sites I want to dive around here, and what I am doing down there (spearfishing most of the time)
Air goes faster at 100'. Light is less brilliant, and colors are washed out. You probably can't see the surface (you might be able to to in the Carribbean, but not around here.) You're VERY aware of where you are, and what you're doing
Don't go beyond your comfort level, and remember that you ALWAYS have the option AND THE RESPONSIBILITY to call any dive if you are uncomfortable - FOR ANY REASON. Any operator or dive partner who won't respect that is one you don't want to be in the water with. Until and unless you're comfortable with diving solo, absolute respect for the right of any party in a buddy group to call a dive must be unquestioned.
I dive off my own boat so I don't have to deal with DMs. But among those who I dive with, the ONE understood rule that anyone who I will dive with MUST agree to is that EITHER buddy can call the dive at ANY time and for ANY reason - or no reason at all. If either partner signals "UP", that's it - the dive is over. If you want to argue with me then you are free to do so when we get back on the boat. Until then I expect you to respect my decision, and I will respect yours if you call the dive as well. We can debate and discuss the rest of the dive plan and profile, but that rule is one that I insist on.
Violate that rule JUST ONCE and I'll never dive with you again.