How can vendors limit the product purchase quantity for customers within the marketplace?

Yes, the vendors of the Magento 2 Multi Vendor Marketplace can limit their customer's product purchase limit. For this the admin will navigate to the back-end settings Stores>Configuration>Webkul>Marketplace>Seller Product Settings. Here, the admin will set the option 'Allow Seller to Add Limit on Product Purchase for customer ' to Yes so the customers can purchase the set product quantity by the vendor.

The admin can also set the default quantity that can be purchased by the marketplace customers if the seller forgot to enter the quantity limit that can be purchased for a product by the customer.

After this, now the vendors under their account panel will navigate to edit/add product page to set the value for the allowed product quantity on product purchase for the customers.