Well all these are scam....You can earn coins by the following ways....
Open the app every day
8 Ball Pool Spin to Win wheel8 Ball Pool Surprise Boxes
Even if you don't have time to play a full round, it's a good idea to open the app daily. Every day you get one free spin on the Spin and Win lever. Spins can earn your coins, cash, or even mystery boxes which allow you to build better pool cues piece by piece. You can always purchase more spins (and sometimes earn additional free spins), but this is an easy way to start building up your coin and cash collection without even playing a round of pool.

Buy a better cue
8 Ball Beginner Cues8 Ball Pool Unlocked Cues
This is a quick way to give yourself an advantage right out of the gate. By using the few coins you initially earn to upgrade your cue, you'll have more success at winning your matches. The first cues you will have access to purchase can give you slight advantages to make you shoot with more power, extend your aiming guides, improve your cue ball control, or increase the amount of time you have to shoot. The more you play, the more cues you can unlock for purchase. Initially the cues you can access are just okay, but as you log more hours and wins you can use the coins you earn in the game to buy cues with some really great benefits.

Use a little English
8 Ball Pool English shot8 Ball Pool English cue ball
English refers to the spin you put on the cue ball when taking your shot. Sometimes you'll have a tricky shot where the ball you want to sink is dangerously close to the pocket. Instead of shooting with minimal power, tap on the cue ball button in the top right corner of the screen. From here you can cap on the spot you want to make contact with on the cue ball. Tapping near the bottom adds backspin, which is handy if the ball you're aiming for is close to the pocket. Tapping near the top adds front spin, propelling your ball forward even after it hits your target ball (handy for breaking). Tapping the sides can help the cue ball move in a desired direction after you hit your target ball, setting you up for your next shot.

English can be a bit tricky to use, so give it some practice. Experiment with different contact spots on the cueball and different ratios of English to power on each shot until you become a full-on pool shark.