You do not have to bid on or buy an item you're not sure about anything in it. If you have any doubts or questions, just ask the seller a question before you bid or use Buy It Now.
For example, you can ask the seller about:
Is this item original?
What are the shipping costs?
Is this item compatible with...?
Has this item ever been used?
Is this item in a sealed box?
On the item listing page, click on the link "Ask Seller a Question" to get a form that will send an email to the seller with your questions.
When you ask a question of a seller, the seller will get an email with your question and your email address. The seller can then write you back an email with the answer. You can choose also to get yourself a copy of the email sent to the seller.