How can I show that a wireless network is vulnerable?

I work with small business owners (barber shops, small restaurant, dr. office, etc.) that do not have an IT staff, but that are providing customers free WIFI, usually just by giving them a password. Most of these setups are consumer grade routers that they are using. Using an app on my phone, in most of these locations, I can “see” other devices (some guest, some the owner’s) on the network and get their IP and MAC address. I need a way to show them how vulnerable their network is (and of course why they should use the solution that I am offering). THEREFORE, I’m looking for a tool/code/app/script that will prove my point. For instance, if I could do any of these things: Get any info (beside IP and MAC) from one of the devices, run a DOS attack on one of the devices for a few minutes, get a screen capture from one of the devices. Again, something that would show the vulnerability, you might have a better suggestion. I would be doing this “test” with the permission of the business owner. I would like this tool/code/app/script to run on (in order of preference, but I will use what every gives me the best proof): Android phone, Windows Laptop, Linux Laptop. If this tool/code/app/script could print out a 1-2-page report (I could get a battery-operated printer) that would be a bonus but not required. For a successful project, I would expect: #1. You will propose a solution (it may be off the shelf, or may be custom). If it is custom, you would deliver the software. If it is off the shelf, I need the software license price (but not the name) in your proposal before I will accept. #2. You will work with me to get it running. I am somewhat technical (i.e. have an app in a phone app store, have written a bit of PHP code, crafted an SMS server/responder, and written some apps in VBA, but I am not a developer/engineer), but will likely have a few questions. #3. The solution will do what you say it will. You would need to tell me what it will do in your proposal. WHEN SUBMITTING YOUR PROPOSAL: Of course a price, but then in notes I would need to know: A. if there will be an additional software license cost and B. what vulnerabilities you expect the solution to show (of course this depends on the network, I get it). END.