Tire Jockey here. I'm currently a 5s manager at an America's/Discount Tire store, I'm happy to help with whatever questions you got.
>Why America's/Discount Tire?
Most of us salesmen genuinely want to help get you on the road safe. We do NOT make commission, so don't worry about us trying to squeeze cash out of you for personal greed. We offer free rotations and repairs for non-customers, and free balancing for customers (with repairs and rotations included.)
>Where should my new tires go if I'm only buying 2?
Whether it's rear wheel, front, or all wheel drive, we always put the new tires, or tires with best tread on the rears to prevent hydroplaning. If you have better grip and traction on the rear of your vehicle, it helps prevent spinning out.
>I've got a nail, should I buy a new tire?
DO NOT REPLACE A TIRE WITH A NAIL! We will take a look at the tire, and repair the tire for free, as long as it can be safely repaired. We will not repair tires that have any punctures on the far shoulder/sidewall. We use a plug and patch method, so if the patch flexes in anyway that is unsafe, there is a chance that the repair can fail, and will fall off as you drive, which can result in a blowout.
>When should I rotate and re balance my tires?
We recommend every 5,000 miles, so we suggest rotating with every oil change.
>When should I add air into my tires?
I personally recommend every 3 weeks. Not only are you keeping air consistent in your tires, but if you have a nail or a leak in your tire, we'll find it much sooner and prevent run-flat damage.
>Are gas station/gummy plugs safe?
They are only safe if you are in dire need. We do not recommend driving on them more than necessary, reason being: plugs shrink and expand with water. When they get wet, they grow, and shrink. If that happens to them enough, they can fall out completely. Company policy prevents us from working on tires that have already been plugged
If you have any questions, please ask. I am happy to help.
