I know this is an old thread, but I wanted to chime in since I almost never pay retail.
Here is what I do to get the most bang for my buck. I use my cc with cash back (only 1%, but it's something), to buy Home Depot giftcards at our local grocery chain. I do this when they are having the double fuelperks (.20 off a gallon up to 30 gallons per $50 spent) deal for giftcards. Every $100 will get us $12 in free gas. I stock up on cards during this time. Then I either buy my supplies online through ebates, which is another 1%.
If I want to price match (can even pm Amazon), I go in the store and show them the ad. They meet and beat it by 10% (I think it was 10%?) AND use my competitor Lowe's coupon on top of that.
One of the managers told me if I want to use my Lowes coupon for an online only HD order, I can call customer service, let them know I have the coupon and they will knock 10% off. I have yet to try that, but will next time I need something that's not in store.
One last thing. Our Lowes is pretty good about marking down an item that is on the shelf but has any damage. There is a guy on the floor who says find him if he is there and he will mark it down before we take it to the register. We have picked up some pretty good deals that way for items where the damage is very minimal or doesn't affect the usefulness of the item. We get bags of concrete, cement, sand, etc for $1 (any size or brand) if it has a hole in the bag. They even help me hunt for the broken bags and one guy offered to put some holes in a couple bags of the higher end stuff to get me a deal. I declined lol.