I rarely haggle when buying unless the condition is not as expected but always have the full amount on hand in case the seller is firm. I also NEVER entertain a 'What's the least you'll take?' kind of offer via email, text, or phone. Haggling only happens face to face on local sales.
Actually, salespeople are usually very reasonable as buyers.
When I was in the car business my favorite question from a buyer was "What's your best price on this car?" I would always answer that my best price is right there on the window sticker. What we need to do is figure out what your best price is.
Several times I would have a man by himself looking at a car tell me that he needed to check with his wife before committing to buy. I would immediately pull my phone out of my pocket and say "Okay, I'm gonna check with my wife to see if it's okay to sell you this car."
I always thought it was funny... sometimes the customer did.