Yes! In fact, Modular Merchant has built in tools for tracking commissions for your product vendors. The commissions, which are earned with each product sale, are referred to as a "royalty". (Similar to commissions earned in a retail consignment environment.) You can follow the steps below to start tracking royalties as products are sold in your store.
Part 1. Create a Manufacturer.
First question: Who's going to be receiving the royalties? To create the user that will be receiving the royalties, we'll need to create a "manufacturer" account. This account will be assigned to one or more products, and it will earn a royalty whenever one of its products is sold. Every product in your store is associated with a manufacturer.
You can create as many manufacturer accounts as you like. To add a manufacturer, go to the Add a Manufacturer area in your store's administration area at: [Navigation Menu > Products > Add a Manufacturer].

Figure 1: The Add a Manufacturer tool is located in the Products menu.
The Add a Manufacturer menu option will open the Manufacturer Editor screen. (See Figure 2 below.) On this screen, you can add a new manufacturer to your store records. Optionally, you can also create an Admin account for this manufacturer by completing the appropriate fields. (See the fields in item "A" in Figure 2 below.) Creating an Admin account will allow the manufacturer to log in to your store's administration area, where they can check the sales performance of their products, and even add new products.

Figure 2: A section of the Add a Manufacturer interface.
Manufacturer Admin Accounts
If you create an admin account for the manufacturer, then they will be able to log in to your store's administration area using the login and password you provide. Manufacturer Admin accounts have their own special home page in your store's administration area. They can only see options related to their sales and their own products. They can also edit their own products and create new ones — so you don't need to be involved in the creation and maintenance of products in your store! (You still can be, if you wish.)
After the manufacturer has been created, it can be assigned to new or existing products in your store. If the optional manufacturer Admin account was created, they will be able to log in to your store's administration area to review their sales and manage the products they have been assigned to.
Part 2. Apply a royalty to the product.
Second question: How much money will the manufacturer be earning? To calculate the commissions earned by each manufacturer, a royalty rule needs to be applied to a product.
To apply a royalty rule to a product, select a product for editing. To do this, locate the product in your store's administration area at: [Navigation Menu > Products > Search Products]. After you have found the product you're looking for, click the "e" edit button to open the Product Editor screen. In the product editor, click on the General Options tab at the top of the screen.
The General Options screen contains the options for assigning a royalty rule to the product. (See Figure 3 below.)

Figure 3: The royalty options in the Product Editor screen.
The royalty can be set as either a flat dollar value, or a percentage of the product's sale price. (If the product is on sale, or otherwise discounted, the royalty will be calculated from the discounted price.)
The product's COGs (Cost of Goods) can also be deducted from the product's purchase price when the royalty is calculated. For example, the 45% royalty of a $20.00 product with a COG of $10.00 would be adjusted to $4.50.
Part 3. Manufacturer can view their royalty earnings on their admin home page.
If an Admin account was created for this manufacturer in step 1, then they will be able to log in to your store's administration area. Their admin home page will include a sales report listing their products, similar to Figure 4 below.

Figure 4: Manufacturer's can log in and review the sales performance of their products.
The Manufacturer Sales Stats report displays the name and the number of units sold within the specified date range. Only the products assigned to that manufacturer are displayed.
Part 4. Manufacturer Statistics report
Store Super Admins have access to a Manufacturer Statistics report. (Located in your store's administration area at: [Navigation Menu > Reports > Manufacturer Stats].) See Figure 5 below for an example of this report.

Figure 5: The Manufacturer Statistics report displays total earning for each manufacturer.
The Manufacturer Statistics report includes sales and royalty information for all of your store's manufacturers. The name, units sold, total sales and total royalty for the specified date range is displayed. This report can be very useful if you send royalty checks to each manufacturer on a regular basis. Note the column with the Excel icon. Details for each manufacturer can be exported to an Excel spreadsheet. See Part 5 below for more information.
Part 5. Spreadsheet report
Detailed data for one or more manufacturers can be exported to an Excel spreadsheet by selecting the checkbox and clicking the Export Selected to Excel button on the Manufacturer Stats report page. (See Figure 6 below.)

Figure 6: The Manufacturer Statistics can be exported as a spreadsheet, which includes even greater detail.
The spreadsheet breaks down each manufacturer's sales, gross earnings and royalties on a product-by-product basis. You can pass this information along to each manufacturer, or use it for internal record keeping.
With just a couple steps you can start tracking commissions for your product vendors. Royalties can be applied to both shipped and digital products. Affiliates can still earn commissions on products with royalties too. If you have any questions regarding royalties or manufacturer statistics, let us know!
_________________
Modular Merchant Mail Bag
Answering your questions, queries and puzzlers.
Modular Merchant shopping cart software, website hosting, and custom programming.