Here's a hint I picked up recently.

If you're on a toy hunt and see something which you feel an urge to buy, leave it on the shelf and wait three days. After that period of time, ask yourself, do you really want it? If you find you now have doubts about whether you actually want it, then don't buy it.

Also try to read toy reviews in the three days. You'll get a better idea of what the toy is like from them than from looking at the box.