I've been closely involved in obtaining and recommending microscopes for students and professionals for many years in the biological, microbiological and medical sciences. Here's my first piece of advice: forget ebay.
Why risk buying what seems to be a bargain only to find that one of the objective lenses is scratched upon arrival as happened to a colleague of mine. It's simply not worth the risk when buying such a precision instrument whether you read the small print or not. If you can't check the instrument out thoroughly yourself before buying, forget it..So what's the alternative?
I've had close dealings over the years with Brunel Microscopes who really look after their customers and provide guarantees on all their microscopes whether they are new or second hand. The prices are very reasonable too and they have an excellent after sales service. Here's a link to their website and I'd suggest you have a look at the new binocular microscopes they stock as well as the "used equipment" section.
http://www.brunelmicroscopes.co.uk/
You've not made clear the subject you're studying and that might well make a difference. For example, if you're looking for a microscope to view geological specimens, there are many geological equipment suppliers on the internet that have microscopes tailor-made for the purpose.
Remember that the method of illumination and objectives/eyepieces of microscopes are often specifically suited to zoological, botanical, geological. metallurgical or other types of specimens. An oil-immersion lens for example will be of no use to you if you're looking at rocks, minerals or metallurgical specimens. The last thing you want to do is to buy the wrong type of binocular microscope.
I'll probably be able to give you further advice if you let me know the nature of the work you intend us