A true warrior has the war won, long before it starts.
The padi books are available to purchase online. Most of your training will be online before ever seeing your instructor.
Can you snorkel, and swim well?
Do you float in saltwater, can tread water or swim for an hour, no touching?
Can you flood and clear your mask while snorkeling?
Can you take off your mask, open your eyes, and swim in saltwater? Above and below surface?
Can you remember to never hold your breath, always exhale?
Do you have the chops to never panic in water with bathtub conditions?
If yes to the above, you'll slaughter your OW training even if the instructor is a dunce.
Hardest part of open water, if you can do the above:
-gearing up
-finding the damn shop or boat. This industry is insanely ignorant on this one.
-donning, doffing, underwater
-getting up the ladder, timing the waves
-air travel
Word of mouth is handy. But any decent dive shop in a 1st world country has a good chance of taking good care of you. (At least until you decide to buy tanks) SB is full of horror stories. Nearly nobody posts about good training
If the class kicks your butt, don't quit or try to get a refund. Muscle through it, learn as much as possible, then fail. Try again with another shop. You paid for the training, at least complete it.
Take a "discover scuba" thing in your local area. Usually just a pool session. Two people in my DS thing actually hated every aspect of scuba. So was money well spent for them.
The lady that instructed us during the DS, pulled us aside afterwards and gave us the finishing test for scuba certification. We passed all the drills before even scheduling training. Huge confidence boost.