When does bulk buying for your bookshop get out of hand?

The listing was for 2,000+ books and I won it for some ridiculously small amount, totally stunned at that as I kept on reducing my top price before I actually put in my bid. When I got there, with my nephew for muscle, there were more like 4,500 books. I know it’s not a lot compared to some other people’s buys but it was a lot for me at the time, bear in mind I was really only starting out and I used to buy a handful of books at a time at op shops and garage sales. I was floored and unable to deal with them for some time.