That's how it's done! I walked into an Office Depot to get a nice office chair for my wife. Asked the manager if there are any additional discounts available, he said no. I then went online and found a $20 off $100 coupon if I order online and pick up in-store. Asked the manager if he'd give me $20 off or if I had to actually place the order on my phone while standing in the store. He said sure. Ended up giving me 20% off instead of $20 and free shipping to get the chair to my house since they didn't have it in stock; only a display model.
This is also how I bought the Cruze. Went to 5 chevy dealerships in the area. Some were willing to negotiate, others weren't. The closest dealer to my house prides themselves in being the best selling chevy dealership in the state, Phillips Chevy. Every time we walked in, they tried to sell me a Cruze with the convenience package. I told them I was very limited on budget and wanted it cheap and the salesman and manager didn't bother to tell me about the Silver Eco they had on the lot without that. Ended up going to Bill Jacobs Chevy and got the car for invoice price minus $500 for GM loyalty.
Put a huge dent in the first dealership's pride when they discovered they lost the sale to a smaller (and based on their attitude, inferior) dealership. When my buddy wanted to buy a Cruze Eco for himself, they pulled the exact same stunt trying to sell him an Eco with driver convenience, floor mats, and cargo net, and he ended up taking them for a ride with negotiations for 2 hours after going back to the dealership I bought mine from and buying the car for a few hundred bucks less from them.
I wonder what will happen if another friend of ours wants to buy a Cruze and we show up telling them they'll lose a 3rd sale to a smaller rival dealership nearby if they don't cut the crap and try to sell us what we need instead what they want to sell us.