If I just purchased an item from your store and I find it coupon that gives me a better discount within 30 days of purchasing this item can I be reimbursed for the difference

I do not work for them. But they have honored this type of policy for me in the past. And this may vary from location to location.

Yes

Yes I am a supervisor at harbor freight, you can come in with your coupon and we will essentially treat it as a return and re-sell the item to you with the coupon applied and refund you the difference. You do not need to bring the item back in with you.

Yes bring it in ask for a manager describe it to them.