We've done something similar, but by delivering pizzas. You can get them talking about you before you come in if you have it delivered, wrapped in gift paper, with a mysterious, clever, anonymous note complementing their pipes. Then drop in and ask if they liked the poster. It will probably go something like, "What poster... oh, the wrapped one? We loved it! Was that from you? Hey Bob, here's the mystery poster guy." Tell them you love their pipes, and that the one on the poster was one of your favorites. Then figure out if they are able to produce pipes faster than they can sell them (if they want to generate more demand). If so, ask what they've been doing so far that's worked, and why. Then you are starting to get at the pain point that you may be able to address, and as you continue asking more of the right kinds of questions, they will eventually want to know more about you, how you can help them, what it costs, if similar clients work with you, etc. I'd need to learn more about you and your goals and customize a detailed flow chart we build for clients at Referable.com. It's a sales flow chart for these types of conversations, leading from establishing rapport to getting to closing a sale on the (typically) second meeting. If you'd like the extra help, schedule a call with me at www.clarity.fm/ryandraving

As a business owner I also feel that for someone to come in and take pictures would feel a bit violating. We've actually had competitors come in and take pictures of our store layout in the past in order to copy.

If you're trying to get their interest with a custom poster relevant to their business, why not use stock footage? For example, I am pretty sure there are plenty of hookah images you can find for free or really cheap and then making it into a poster would give you the same results.

It's often easier to gain a new client by providing concepts or proofs up front (if you can afford the time and expense as a marketing cost) rather than attempting to explain what you "could do" for them. You do seem to have answered your own question in our explanation. If you've done it with success, why alter your approach? You have validation from your own experience.

Many creative-field freelancers use this technique to score new clients and gain referrals. A word of caution, however - public spaces like a hookah cafe are one thing. Private facilities are another. Expect at some point to have it demanded that you turn over the images or have someone refuse to allow you to "use" the image(s) in promoting your business if it includes their brand or IP in a manner they don't feel is consistent with their brand identity or implies an endorsement.

Feel free to reach out with any other growth hacks you're considering. I'll be happy to give you a quick thumbs up/thumbs down and why.