BEWARE - as a half.com buyer and seller, I want you to know that most sellers ship books via media mail - ie SLOW. You can choose to pay more for priority mail, and in my opinion if you need the book in the next few weeks it'd be a wise investment.
Books I buy for fun-reading I don't mind waiting and just pay media mail, but the textbooks I bought used I made sure would get here on time. I have had books ship from clear across the country via media mail, and take almost a month to get here. On the other hand, just last week I bought a book and paid for priority mail and it came from clear across the country in 3 days.
I've never had a problem buying used books and having to deal with highlighting issues. I just read the description, quality, and seller rating before purchasing. Most sellers don't want their rating tarnished so they're careful to exactly describe the condition or even under-rate it so you'll be happy when it arrives.
Half.com has new customer coupon codes which are a good deal. You can get those codes from http://www.bigbigsavings.com
- just search for half.com and they'll pop right up. Good luck!