I bought all mine off booko while studying. I found the easiest way was to look at the book cover at the uni bookshop and then check the booko cover and the ISBN number were the same. I never ran into trouble with any of my books. I had some that were packs, some that were Australian editions etc and they were all fine.
It took 2 weeks for me to get them max. Usually it was about 7-10 days for delivery. I LOVE booko- I have saved SO much money from shopping through them. Unless it is a new edition of a book, check ebay and other places where you can get them second hand. A lot of people sell theirs in excellent condition and it will also save you some money
In first year I bought all mine new (through booko) but 2nd and third year I bought 2nd hand when I could and they were always in great condition.