Pre-Transaction Fraud Detection: How to Catch Bad Actors Before Payment

Pre-transaction fraud detection is the practice of evaluating risk signals before a payment is processed. Rather than catching fraud after money has changed hands, when chargebacks, refunds, and evidence gathering are your only options, you block it at the door.

This approach is both cheaper and more effective. A prevented transaction costs nothing. A chargeback costs $150+ when you factor in the fee, lost product, and operational overhead.

Why Pre-Transaction Beats Post-Transaction

Most payment processors offer some form of post-transaction fraud detection. Stripe Radar, for example, evaluates transactions after they're submitted. This catches the most obvious fraud, but by the time a chargeback is filed, you've already:

1. Lost the revenue, The transaction amount is clawed back.
2. Paid the chargeback fee, $15-$100 per dispute, win or lose.
3. Delivered the product, Digital access consumed, physical goods shipped.
4. Spent team time, Hours gathering evidence for the dispute response.

Pre-transaction detection eliminates all four costs by stopping the transaction before it starts.

The Pre-Transaction Signal Stack

Effective pre-transaction detection layers multiple signals. No single signal is definitive, but together they produce a reliable risk score.

Email Signals

IP Signals

Behavioral Signals

Implementation: The Two-Call Pattern

The most effective pre-transaction pattern uses two API calls, one at signup (email validation) and one at checkout (full risk assessment):

Call 1: At Signup

curl -X POST https://fidro.io/api/validate \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{"email": "customer@example.com"}'

Block disposable emails and invalid domains immediately. Store the validation result on the user record for later use.

Call 2: At Checkout

curl -X POST https://fidro.io/api/validate \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{"email": "customer@example.com", "ip": "203.0.113.42"}'

Add the IP address for geolocation matching, VPN detection, and a combined risk score. Use the score to decide whether to process, review, or block the transaction.

Decision Framework

Based on the composite risk score:

• Score 0.0 - 0.3 → Process normally. Low risk.
• Score 0.3 - 0.6 → Process but flag for monitoring. Review if a dispute is filed.
• Score 0.6 - 0.8 → Add friction. Require phone verification or additional identity confirmation.
• Score 0.8 - 1.0 → Block the transaction. Redirect to a support contact form.

Start with these thresholds and adjust based on your false positive rate over the first two weeks.

Running Checks in Parallel

Pre-transaction validation should not slow down checkout. Run the fraud check in parallel with other checkout operations:

const [fraudCheck, inventory, tax] = await Promise.all([
  fidro.validate(email, ip),
  checkInventory(items),
  calculateTax(address),
]);

if (fraudCheck.risk_score > 0.8) {
  return res.status(422).json({ error: 'Transaction blocked' });
}

With a 200ms average API response time, the fraud check completes before the database queries return.

Getting Started

1. Sign up for free, 200 validations/month
2. Add email validation at signup to catch disposable emails immediately
3. Add IP validation at checkout for geolocation and VPN detection
4. Read the API docs for the complete risk score breakdown