In the past, I occasionally combined merchandising projects with other jobs along a route. This is not a guaranteed way to increase your hourly equivalent revenue. It is just one thing to consider as you go along and become familiar with job types. In the worst case scenario, you will encounter some condition that will slow you down to the rate of one job per day and make you want to tear your hair out. In the best case scenario, you will get your momentum and have days where work flows, you have time to breathe, and you can do additional jobs.
What about your comfort with the job? (After an auto accident this year, my back became unreliable and was injured twice during merchandising and other jobs. I now do only easy-for-me assignments. There are plenty of other assignments for someone who has the backbone for the job. haha.) Is your back in great condition? Can you stretch, kneel, squat, use appropriate pressure, carry and balance objects, etc.? If so, you might have the kind of back that is useful in merchandising. This leads to the idea that as you go along and become efficient in the work generally, you might be able to add mystery shops or other assignments and build routes or better-paid work days.
Speaking of routes, where do you live? (rhetorical)
One recent merchandising job took place in locations that were well-spaced along a major highway at the rate of at least one per suburb, or approximately twenty minutes apart from each other. If you could access this type of project and you could perform your task efficiently, you could perform multiple merchandising tasks in one day along with other, nearby shops.
If you stick close to home and home is rural or small town, you might enjoy recurring tasks. Some people perform recurring tasks in the same store and work there many times per month. I don't know what they are earning, but they are not incurring much travel expense by working this way. Their revenue appears to be additive.
Why not give it a try and find out whether it will suit you?
Bach is not noise, Madam. (Robert, in Two's Company)