I want to buy MS Office 2007 or 2010 Professional and I can find it on Ebay at an average price of $175 US. I am wondering if there is some reason I am not aware of to not buy any of these programs. What do I need to know to make an informed decision?

Get OpenOffice -- it is free and compatible with M$ Office.

Generally speaking, buying on eBay is the same as buying anywhere else if what you are concerned about is getting a genuine product: if the price seems too good to be true, it probably is.

Make sure too that would would infact be purchasing physical disc medium to install. Way too many Microsoft products being sold on EBay end up being nothing more than a generic OEM volume license key they send you with a link to Digital River or some other online source to download your product and install. No disk. Problem? Yes. If you ever re-format and re-insall, that "product key" you bought was a once and done deal for installation and is not a true product key that can be used again. Even if you (as I did) burned the downloaded .ISO to a DVD and kept it. I got an exclusive "Student deal" on Windows 7 for $70.00. Thought it was too good to be true, but it worked. Only to find out my legitimately legal student price deal I bought online was a once-and-done product key/download.

Now I did after making a few calls to India and some noise, get them to re-issue me a new Product Key that is full retail key (meaning install as much as I need on upgrades/reformat-reinstalls). But it was a huge hassle. All because of one online deal that was cheap.