I've done about 20 of these in the past 3 months.
Note that although Sears now owns Kmart, the actual audits are slightly different.
If you audit Sears, they have to provide someone to accompany you within 15 minutes of your arrival. If they don't, you are free to start the audit yourself. If you start it yourself, you won't have a remote scanner, so you need to grab a cart and your items, then take them to a register to scan them. They are supposed to provide someone as soon as they can, and they normally do because they don't want it to go on the audit that they didn't provide anyone.
If you do a Kmart audit, it is different. You have to wait. If I remember correctly, there is even a limit to the time you have to wait. If no one shows up in the time frame, then there is a # to call at Kmart. If you can't get a hold of the Kmart person listed in the authorization letter, then there is a phone number to call someone at the MSC. This is all in the instructions.
The important thing is that if someone goes with you, they have a remote scanner with them so it goes faster than picking 100 items and taking them to a register.
Regarding the length of time it takes. The first one you will be slow. I would totally plan on at least 3 hrs the first time. After you have done a few, your time will improve. I actually did a Sears Auto Center audit first because you have to scan only 25 items. That was a useful primer for the bigger audits.
I would never bother to go all the way back to the office to work out the game plan with whoever is walking with you. But I do go over the game plan with the person who is walking with me when we start at the customer service desk. That's because they will know how their store is set up and what is the most direct route. Especially since you also have to test the public-use price scanners, plus the ADA audit. Might as well pick those up along the way.
There are some things that you can't pick out in advance, like clearance items. That's because no one knows what's been put on clearance until you get there. In my last three audits, 20+ of the items I was to audit in each store were clearance items. True you get the category (department) in most cases. But you can't pick the actual items until you get there.
I do think it is helpful if you can "create a plan" with the walker. That makes them feel like part of the team and they will help you get done sooner by suggesting a good path through the store. Mind you, they aren't to stear you towards product. You pick the items - that is a must. But they know how the departments line up next to each other.
The other thing I do is let them know the record time a Kmart or a Sears has been done in with me. I have always found they are anxious to beat the best time so far. :-)
Regarding pay, those audits fly off the shelf here for $25. I'd be thrilled to get $40 for them.
Regarding paperwork. The Kmart paperwork is easiest. You have to fill in the details on the problem items, but you don't have to upload anything except the audit authorization. The worst i've seen is 7 mispriced items, and sometimes they have no mispriced items.
The Sears paperwork always requires scanning and uploading the forms, except I think when there are no bad prices. It's been a couple of months since I did a Sears audit, but I am pretty sure this is true.