Let them go first
Ask "What's the best you can do?" before you name a number. They may start lower than you would have.
When it works
When you do not know what a fair price is, or the seller has room you cannot see.
What to say
“What's the best you can do on this?”
The mistake to avoid
Throwing out your own number first and finding out later they would have gone lower.
Practise it
Try this move on today's made-up shopkeeper in Bargle. Two minutes, free.
Play today's haggle