My experience with pricing audits at smaller stores like gas stations and drug stores is that there's a great chance that you are going to be stopped and possibly kicked out. In my case, I was not paid after being kicked out. Remember, you are being asked to go into another business, without their consent or knowledge, and do a thorough audit of their inventory and pricing. What makes it look egregious and somewhat sketchy to the business is the fact that so many pictures are required. Having someone walk around your business for an hour taking dozens and dozens and dozens of photos all over without consent seems unethical to me.
If I was a business owner or a manager of a location and I saw someone attempting to do that, I would tell them that I would be happy to help them find what they are looking for. If they told me that they were doing a pricing audit, or I can tell by watching them that they were doing one, I would slightly tell them to leave if they were not buying anything. In that case, it's loitering, and that's a common and easily enforceable rule at businesses.
Of course, I would be civil about it, but some business owners and managers might not be. You might get accosted with foul language or have the cops called on you. I know shoppers that have tried these that have had both of those things happen. So just remember, this is what you could possibly be dealing with if you decide to sign up for one of these shops. I hope you make the right decision.