What is saving retail now are security cameras from shoplifting, it seems to be the only evidence that the courts are accepting. However, have a read here on monitoring and the law if you have or intend to have cameras.
For retailers, the best security systems are those that are directly connected to your point of sale software. With such a system if for example, a customer said, I gave you a $50 and you gave me change from $20, well you just press a button on the cash register, find the transaction and playback it back. Every till should have one.
However, there are many more places to cover than the till for example the shop itself, the front and exit of the shop, the back room and some parts outside. For these often you need wireless security cameras.
They have one great advantage that they are easy to move around. However unlike wired security cameras, wireless security camera are funny things, you install in one shop a few and they work perfectly, you put the same cameras into a similar shop and it is nothing but trouble so we have to pull them out and replace them.
Here are some points
Map out your requirements on paper.
Do it carefully as I assure you that paper will get a lot of use. Try to draw it to scale if possible.
Now, put on the paper where you feel the cameras should go, generally, to save cost people follow the power points as much as possible.
Now measure the range of these camera positions to your camera base. You will need to know the range before you can buy the camera. What you also need to determine where you will need a narrow vision and where you need a wide-angle camera. If you are not sure the salesman can tell you what cameras they have for such range and angles.
If you are in an area of a lot of WIFI you need to make sure that it will operate in these areas. I have seen WIFI security cameras fail in shopping centres.
You want cameras that are easy to install and setup. Over their lifetime, you are going to want to move them around. This, after all, is the point of having them wireless.
Most important it is easy to change the Date and Time, you do not want to have to try to explain to a judge why the alleged robbery took place at this time but why your camera showing a different time. If you are in an area that has daylight savings you, make sure your camera has daylight savings enabled and check to make sure it does automatically adjust the cameras time.
I would say 1080p should be the standard resolution that you should use. With prices today there is little savings going much lower and often you need that extra resolution. Remember a shoplifter can be out of your shop in seconds and you need often to make an instant decision.
Check how good the motion cameras sensor is, you do not want lags.
Make sure the camera got decent night vision, you do not want anything that looks grainy. Some of these cameras have a function that I love when it is dark a red light like a gun shines out, it helps to deter undesirables as they can see the cameras are working.
Much of the camera software supplied by the security companies are full of bugs. I would not count on it despite what the specifications say.
How much to budget?
Impossible to say for the $800 they spent it was much for what they need, others that spent $20,000 will sigh and say that it was not enough.