So let's say you're selling a car. Somebody offers you $100 bucks to hold it for them for a week while they research the car to see if it fits thier needs. During that week you have two other interested parties look at the car, but you tell them you are holding it for a week for someone else.
The week ends, and the original person who asked you to hold the car says, "I need more time". Would you really continue to hold the car for them? You could end up holding the care for another week or two and then still be stuck with it when the person walks away.
On the other hand, you could tell them, I'm no longer holding the car for you. I have two other people interested in buying this car. I will sell to the first person who makes an agreeable offer. This now puts you in a position of control. If this person is really serious about buying the car, you will force them to step up and buy it. If they are not serious, then they most likely wouldn't end up buying it anyway. and meanwhile you have others making offers that just might trunp what the first guy was willing to pay anyway. I'm not sure why everyone thinks this is "horrible". Not to mention the fact that this should have been expected since the Chinese are known for dragging out negotiations as a technique to try and get a better deal.