Before buying any item on Email, I always gather information from other areas about the cost of the item, if there are different types of the item & which one would suit you the best.
If I can find the item in the shop, I go and have a look at it, jot down any code Numbers or Item Product Number of the one that I am interested in.
Also search all areas of Ebay by typing in different words for the same article, it is surprising how many people put one letter out of place so you might miss it, its these ones that you will properly get a good bargain with.
Always write to the person about any questions at all you have about the item.
Then if you have done your research, when you go to bid on any item you know what you are getting and how high a price to should go.