Iphone off ebay a good idea?

Do you think it would make a difference if i got an iphone on online ebay, verses buying a new one, what sucks is i've been with sprint since 2008 and if i wanted to buy an iphone with out an upgrade is 800 and with an upgrade you still have to pay extra, i'm seeing all these iphones between 200 too 300 dollars and that seems kind of good?

Well i got mine for $99 at Verizon

You can get good deals on ebay, but some caution is always needed. Always check the seller feedback. Lots of negative feedback should cause alarm bells to ring. Also, if something like cash on delivery is possible, you should ask the seller for that. It costs you a bit more but guarantees you get your purchase.

I'd highly recommend not using ebay. I'd recommend amazon over ebay. If you want though go ahead.
A few basic keys to watch for though is where it comes from. If it comes from China, Taiwan, Japan or another country I'd probably not get it. Nothing against those countries, most commonly they have fake items listed on ebay though from those places. If there's not any direct pictures of the phone, only stock pictures I'd highly recommend not getting it. Make sure you see the actual phone itself I'd also pay attention to the buyers feedback. Some feedback is fake to make people look better sometimes. They'll pay somebody to "purchase" an item and leave a good feedback. Next, look at the details and condition, what the phone actually is make sure it is not broken or for parts only, but is nearly new, good quality, and working. Feel free to ask the seller about the phone too as wel. Another thing to watch is make sure that the shipping is ridiculously high. Some sellers will put an iPhone at $250 and say Cheap great price. But then list the shipping cost as $250+ so your paying $500+ still. Also I'd recommend buying only from people who have a return option, most commonly if there's no returns then it will be a fake iPhone. So go ahead if you want. Just have some caution to buying on there.