How do you evaluate if a product is underpriced across different sellers before sourcing inventory?

Hey everyone,

I’ve been experimenting with different ways to evaluate sourcing opportunities before committing to inventory.

One thing I noticed is how much price dispersion there can be between sellers listing the same product across different marketplaces.

To explore this, I built a small spreadsheet model that aggregates listings of the same product and calculates things like:

• average market price
• how far each listing deviates from the market
• a simple seller reliability score
• estimated margin after marketplace fees

The goal was simply to see if it was possible to identify potentially underpriced listings faster than doing everything manually.

I tested the idea using a small dataset of iPhone listings just as a proof of concept.

I’m curious how other sellers here approach this problem when sourcing.

Do you mostly rely on manual research (sold listings, comps, etc.), or do you use any tools to evaluate pricing differences?