Do things like free shipping if you spend X amount get you when you were only looking at one thing? Or percent off sales if you order by X date?

I am an almost exclusive online shopper due to store scarcity in my area. I feel like I get scammed a lot because it's hard to pass up a 45% off deal. You know when you think, why not buy a few more things since it's 45% off. Or the hardest one for me to resist is the free shipping for ordering a certain amount when I only planned on buying one thing and it doesn't meet the requirement. If I was standing in the store, it would be so much easier to just buy one thing and go.

Do you capitalize on such "deals" or is it a scam like it seems? What game plan do you use with online ordering?