I haven't ordered from them in a few years. In the past, the orders always arrived. Overstock is somewhat known for less-than-stellar customer service.
As long as you don't have any issues with what you order, it is no problem. I don't think you would have any issues with books and rulers. I would probably order these from them.
You can go to ResellerRatings.com and check the reviews of hundreds of different shops.
Overstock.com's page is here:
http://www.resellerratings.com/store/Overstock
I wouldn't rate them as low as this does, but people are always more likely to take the time to complain.