It has been peak season teaching English, so I have, sadly, been too busy to dive for too long. However, I have had quite a few students try scuba diving and even get certified during their respective stays in the Philippines. This has allowed me to at least talk about scuba diving during my extended surface interval.
While it is understandable that students would seek out the least expensive dive centers, I have discovered that there are some outright dangerous dive centers around. I actively warn my students about these dive centers, but seemingly to no avail. Fortunately, no one has drowned yet. Unfortunately, I think this is merely because luck has been on their side.
Of most concern, is learning to share air with a fellow first-timer. I learned to share air with a professional instructor, who was ready for every eventuality. Consequently, I had a safe experience. Many of my students, however, told me stories of swallowing considerable water because they and their inexperienced partners made mistakes.
Perhaps you could argue that it is good to train with others, because you never know who you might have to share air with in the real world. I agree. However, I would counter-argue that you should practice first with a professional, become comfortable with the exercise first, and then practice with others. The fact that they swallowed considerable water and I swallowed none indicates to me that my training was considerably safer than theirs.
I think the number one sign that you should avoid a dive center is when you see photos of guests molesting marine life. Whether this means removing sea stars from the ocean or agitating pufferfish or whatever, violating the “don’t touch anything” rule is a good sign that they only want your money. And if money is priority one, safety necessarily isn’t.