From reading this forum and just recently now, saying something, I've learned a lot about the part of mystery shopping (and everything in between). One of the most important aspects is that each shopper is conducting themselves as a business entity separate from the MSC.
With that in mind, accurate records of each shop performed is paramount.
For invoicing and followup payment, I've commented before. But, here are a few other things to do:
1. Create your own worksheet or what others have referred to as a "cheatsheet". Make it tailored to each type of shop that you do. Have reminders or some form of note on it of the parts of the shop that the MSC wants to know about. That could be required photos , names, etc. Make sure you fill out the worksheet immediately after performing the shop. I learned that the reason a cop sits in his car long after he has given the ticket to the motorist and the motorist has left is because he is filling out his report while its fresh in his mind.
2. If you are supposed to get receipts to prove you performed the shop, make sure you have them and make sure you photograph them immediately after performing the shop. Do this while filling out the worksheet. Keep a small stapler in your car. Staple those receipts to your worksheet.
3. File the worksheet after invoicing the MSC. File the worksheet in a folder for the month the shop was performed. For me, I just label the file folder, for instance, as "March 2016". All of the shops that I performed and invoiced for that month are filed into that folder. I've heard that others keep separate folders for each MSC in which they worked. whatever works!
4. I track my payments by checking off my worksheet that I've been paid for it. Maritz is a good MSC as their check that arrives lists the shops or "visits" as they refer to them. I open my file, and start checking off the visits and worksheets in which I've been paid. If I find a visit that has not been reimbursed, I call the company and pleasantly ask why. Usually there is a good reason and we (the MSC and myself) work to resolve the issue.
None of these ideas or actions I've described are of my own design. They are of the ideas I've found on this very helpful forum.
Like I've said before, keeping track of your shops is good for your business and good at pay and tax time.