Can we allow tax-free sales for certain sellers who qualify with a resale certificate?

In the MultiVendor app, by default, we provide the option on the product form, where the admin or the seller can exempt a product from tax, simply edit the product and uncheck the "Charge Tax" option. This ensures no tax is applied to that product at checkout.

Refer: https://webkul.chatwhizz.com/share/screenshot/67c98927decbc80572ce8ae7 

Additionally, regarding tax exemption for businesses with a resale certificate:

Tax Exemption Based on Tags: You can now exempt customers from paying tax based on the tags assigned to them. This means you can enable or disable the Tax Exempt option for customers according to their designated tags.

• If a customer tag is exempted: Customers with that tag will not be charged any tax during checkout.

For detailed information, please refer to this guide: https://webkul.com/blog/shopify-multivendor-marketplace-slot-pricing/#tax-exempt