Olympic Bars are not created equal, that is a fact. Ensure you purchase an Olympic Bar fit for purpose.
If you are doing weightlifting, like snatches, clean and jerks etc. You will want a really good olympic bar, made form high alloy, with needle bearings. The more needle bearings the better, this will mean better lifts, as the sleeves rotate smoothly. These bars are also suitable for dropping with rubber bumper plates (not normal plates)
If you are doing bench press, deadlifts and squats. Workout the maximum weight you would ever do. I.e. If your max weight is 100kg, it is not necessary to buy a bar with a max load of 680kg. If you buy a bar and exceed the max load, you will certainly bend the bar.
Make sure you look at the type of steel that an olympic bar is made from. If you overload lower grade steel, you will most likely bend the bar and it will stay bent. High Alloy is the best steel. It will bend under high load, but will straighten. Lower Grade Steels are A5, Q235, Spring Steel Sits in the Middle, High Alloy is the best. Remember buy a bar fit for purpose. If you do not require a bar for heavy loads, then lower grade steel may be sufficient.