So... Obviously "second hand" ebooks is wrong. It accounts to piracy.
Generally I believe it's accepted that second hand classics are generally OK. Such as a second hand copy of royal road etc....
So where do we draw the line?

Is it ethical to actively look for second hand versions of books released in the last 10-20 years since they're cheaper?
If someone (a friend) has bought a pdf ebook and printed it off, and you know that because of there age there is no chance that they will use the digital copy again and they offer to give/sell it to you, is it ethical to buy/take it?
If its ethical to pass on some in print lecture notes, then is it also ethical to print off some purchased lecture notes and pass them on if you don't plan on using the original copy again?

What about sharing magic books?
If I bought Card College 5, and a friend wanted to borrow it, would it be ethical to lend it to him?
Or if we both decided to buy it together and each pay half?
(this scenario is made up btw, just wondering what you all think)

I'm just wondering what people think, since when I buy fiction I normally go for the cheapest I can get it since I'm a student, but tend to stick to second hand print books that are old, or brand new modern-ish print books. What do people do?

How so? A can give B a purchased PDF file. Not copy, just give, not retaining a copy.

I would suggest researching copyright law, and searching this section of the Café for that topic which has been discussed at length prior. Think of it as second hand thoughts.
As long as you don't make copies of it to distribute...

Didn't think of it like that...
I've always considered sharing any digital files to be piracy if you don't have the rights to...