---
title: "Sales Tax for Online Sellers: Nexus, Marketplace Rules and Staying Compliant | Capstone CFO"
description: "A plain-English guide to sales tax for online sellers: economic nexus, marketplace facilitator rules, registration and how to manage compliance as you grow."
image: https://capstonecfo.com/hubfs/capstone-2026/insights-covers/sales-tax-for-online-sellers-nexus-marketplace-rules.png
---

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Insights

# Sales Tax for Online Sellers: Nexus, Marketplace Rules and Staying Compliant

Capstone CFO

**Short answer:** Since the Supreme Court's 2018 Wayfair decision, states can require online sellers to collect sales tax based on sales volume into the state, not just physical presence. Marketplaces such as Amazon generally collect tax on sales made through them, but sales on your own website are your responsibility. Track where you have nexus, register before you cross thresholds and automate collection and filing.

## Key concepts

- **Economic nexus:** an obligation to collect tax once sales into a state pass its threshold, commonly around $100,000 in annual sales, sometimes with a transaction count.
- **Physical nexus:** inventory in a warehouse, employees or offices in a state can also create an obligation.
- **Marketplace facilitator laws:** marketplaces generally collect and remit on sales made through their platforms.
- **Taxability:** some products are taxed differently, or exempt, depending on the state.

## Where online sellers get caught out

- Inventory stored in third-party warehouses creating nexus
- Crossing thresholds in several states without noticing
- Assuming marketplace collection covers direct website sales
- Not tracking exemption certificates for wholesale customers
- Exposure discovered during a sale or financing diligence

## A compliance routine

1. Review sales by state monthly against thresholds.
2. Register in states before you cross a threshold.
3. Use tax automation software connected to your store.
4. File on time and reconcile tax collected to tax remitted.
5. Assess past exposure and consider voluntary disclosure where needed.

## How Capstone CFO helps

- Map your nexus footprint by sales and inventory location
- Set up and connect sales tax automation such as Avalara
- Reconcile tax collected, filed and paid each month
- Quantify historical exposure and coordinate with tax advisors
- Prepare clean sales tax records for buyers and lenders

## Frequently asked questions

### Do I have to collect tax in every state?

Only in states where you have nexus and that impose sales tax. Several states have no general sales tax.

### If Amazon collects tax, am I covered?

For sales made through Amazon, generally yes. Sales on your own site are your responsibility.

### What if we never collected tax?

Talk to a tax advisor. Many states offer voluntary disclosure programs that can limit penalties and look-back periods.

*This article is general information, not tax advice. Sales tax rules vary by state; review your situation with a qualified advisor.*

*Unsure about your sales tax exposure? See [how we support e-commerce and digital retail brands](https://capstonecfo.com/e-commerce-and-digital-retail) or [book a call with our CFO team](https://capstonecfo.com/meeting).*

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Talk with our CFO team about your goals.

[Let's Chat](https://capstonecfo.com/meeting)

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- [Fundraising Readiness](https://capstonecfo.com/solutions/fundraising-readiness)
- [Exit & M&A Readiness](https://capstonecfo.com/solutions/exit-and-m-and-a-readiness)

#### Who We Serve

- [SaaS & Software](https://capstonecfo.com/saas-and-software-companies)
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- [Professional Services](https://capstonecfo.com/professional-services)
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