Is it ok to buy/use this

What do you intend to do with it? Are you overclocking a CPU to an extreme or something like that?

If you're not overclocking, then there is no need for such an expensive cooler.

I'm not sure if a refurbished H100 is even worth $100. That seems rather similar to its price when new.

I'm going to overclock an i7 3770k. The refurbished one is $30 cheaper and since im still a teen, I don't have that much more money. The MAX that I can spend is $100 no more.

No need for such an expensive cooler for the i7-3770K. It won't let you overclock it much better than even a much cheaper cooler such as a Tuniq Tower 120 Extreme or if you must stick with water cooling, say a Zalman LQ320 or such.

I'm not a water cooling expert, so maybe there are even better water coolers at decent prices that I'm not aware of. I can say with decent certainty that water cooling doesn't cool better than oftentimes much cheaper high-end air cooling unless you make a good custom loop.

Have you already bought the i7? I know how hard money is when you're young, and I figured I'd let you know that when you're gaming, there's no difference between the i7 and an i5 for $100 less. (Games can't / don't use hyperthreading, which is the only difference between the two chips.)

That being said, what sort of overclocking are you looking to do? There's virtually no scenario where I'd recommend a closed loop water cooler except in something as extreme as a Falcon Tiki.

Buy yourself a Hyper 212+ and an aftermarket fan - I like Corsair's. You'll be able to hit a 4.4-4.6 GHz overclock easily, depending on the roll of the chip you got.

My neighbor works for intel so I got employee store access. I paid $105 for a 3770k. Although I love the advice, no one has answered my initial question of if it is safe to buy a refurbished h100 rather than a new one. Will there be any difference?

The difference is that someone used it and returned it. It might be defective, it might be fine. We can't guarantee that a refurb unit has as good of a chance of working properly as a new one. If it works, then it should be like new. If it doesn't work... Let's just hope it doesn't get the rest of your system wet  

* Whistles.* I want that kind of a deal!

That being said, it's as safe as any other refurb - it might be in perfect condition, it might be about to die. You can't tell.
(And again, the H100 is a bad pick anyway; there are cheaper options that cool better, even factoring in the refurb price.)

There WILL be the risk of it not working. Spending 100 dollars for the H100 for you is a waste of cash. It's better spent saved for a new GPU.

There's no reason for you to even overclock very heavily if you're only using 1 GPU too.

Buy this heatsink, it's more than enough for you:

http://www.amazon.com/Cooler-Master-Hyper-212-RR-212E-2...