If you're sure that the 7D is in good shape that's a decent price. If you're ok with a bigger heavier camera then it's a good one. That said, if you're ok with lightly used I'd get a refurbished Rebel T3i from Canon for $350 or so. If you're determined to spend money put it towards lenses, not a fancier camera body. The Rebel cameras are good cameras, have a lot of features that beginners like, and will save you some money over more expensive higher end cameras with features you might not use. The image quality is pretty similar; lenses will have a much greater impact.
Honestly.... "heavy" is considered a benefit. When shooting you need to be "steady". It turns out the sheer mass of the camera provides some inertia -- and many people find the heavier cameras tend to be less shakey than lightweight cameras. Some photographers put battery grips on the bottom of their cameras just to add weight.
The biggest problem with weight is the comfort of the camera strap. The factory strap is a neck strap. If you walk around all day wearing that strap it wont be very comfortable. "Sling" type straps are worn like a sash... strap on one shoulder and the camera hangs on your opposite hip. The camera slides up the sling when you bring it up to your eye-level to shoot. But the big advantage of the strap is that it's comfortable enough to wear for hours and hours without feeling fatigue or irritating your neck.
The 7D will have better "performance" for action photography.
The 70D will be a bit more "user friendly" for entry level photography.
The cameras have nearly identical focus systems (both have a 19 point AF system using the same layout pattern... although you can do a few more things with the 7D such as put a focus point into "spot" focus mode.)
They have similar (but not identical) control layouts... having both a front control dial and a rear control wheel (Rebel bodies do not have the second wheel at the back of the body). They also both have a top LCD with a few instant-access buttons to features commonly needing adjustment. The Rebel bodies do not have the second LCD screen on the top of the camera. This second LCD screen with more instant-access controls are found in the higher end bodies but not the entry-level bodies.
However... assuming you are willing to buy a couple of books and will read them through and practice photography... or take some classes... the 7D is probably ultimately the better camera for an experienced shooter (or someone willing to take the time to learn to use it.)
The 70D will be more user friendly toward beginners. It has the scene modes where the camera is basically automatic (all cameras have a full-automatic mode) but the scene intelligent modes optimize the exposure settings based on what sort of image you tell the camera you're about to shoot. E.g. it does "landscapes", "portraits", "action", "night photography", etc. etc. The 7D does not have these features because all these features do is adjust the exposure settings to optimize to those conditions and experienced shooters already KNOW how to optimze the camera to those needs (they don't need those modes and would probably never used them even if they had those modes.)
Honestly.... "heavy" is considered a benefit.
...to some. Others like lighter cameras. It's a subjective quality. The inertia claim is mostly theoretical unless you're claiming that the heavier body dampens vibrations to a measureable degree. I know many photographers would like to think it's more stable, but placebo can be a powerful pill. I could just as easily argue that fatigue will set in faster with a heavier camera and will in turn lead to shakier photos. In reality, I don't think weight has a measurable impact on sharpness.
I will agree that heavier cameras feel better with heavier lenses, but that's a balance issue, not inertia. And conversely, I love using my little rebel with small primes for travel. Again, it's subjective.
For the price difference I would not hesitate to get the 7D which is a better built camera despite its age. For the same price I'd get the 70D. By the way if you use a 70D built-in flash with a 24-105mm lens with hood, the hood will interfere with the picture...quite a disappointment for such a camera.
lacieleigh, Obviously the used camera looks attractive but the new camera is worth more because it carries a warranty and the promise that it is new.
As a brand new user, I wouldn't expect you to be much beyond an exploration stage of your photography. Still photography is a wonderful art form and, for many, encompasses the entire world of photography. But, IMHO, you should not dismiss video photography too hastily. DSLR video takes the wonderful variety of lenses available and lets you use techniques that were previously unavailable to consumer video photographers. Where shallow depth of field techniques were the exclusive province of professional videographers, anyone with a 70D and a fast lens can now film with the same effects.
I mention this because the 70D was designed as much for videographers as still photographers. The revolutionary dual pixel autofocus capabilities are meant to benefit the photographer when focusing in live view (using the screen, not the viewfinder to focus) mode and video recording.
I'm not agressively promoting the 70D but I am advising a cautious and measured approach to this wonderful form of art. I would advise anyone new to photography to spend more time, money and energy on learning the art and resist the urge to dive into the deep, and expensive, end of photography before getting familiar with the practice. Both 7D and 70D are at the "deeper" end of Canon's line of consumer cameras.