A brand reviews its arbitrage seller activity and finds the same names it saw a quarter earlier, across different SKUs. A test purchase could trace where the stock originated, but with dozens of sellers to investigate, purchasing from each one would not be efficient.
Most brands therefore end up playing whack-a-mole with a test purchase. The parcel arrives, the trace stops at a reseller in another country, and the list is as long as before.
Online Mind allows brands to replace this reactive approach with prioritized, targeted test purchasing. By monitoring seller activity across products, platforms and over time, brands can see which sellers keep appearing. A continuing presence points to a continuing supply of stock.
This post answers: which arbitrage seller most likely has a continuing supply of the product, and is therefore worth a test purchase?
To find out how to prioritize which sellers are worth a test purchase, the post uses the Most Frequent Lowest Seller (MFLS) metric as a stock indicator: a seller who repeatedly holds the sole lowest-priced position on a listing has units to sell repeatedly. The purpose is to trace where the goods come from. Then four criteria narrow the list: how many SKUs and platforms the seller appears on, how many weeks it keeps showing up, how relevant its products are, and whether it is on your dealer list. Once the parcel arrives, the post walks through what a test purchase reveals and what to do with each of the four possible outcomes, each decided by the brand based on the goods and its own distribution structure.
The same product keeps reappearing, on other SKUs or under different seller names. Most of it is lawful cross-border trade in genuine goods. For these cases, a price alone says nothing about whether a seller did anything wrong. Other situations involve counterfeit goods, and only the goods themselves show which case you are looking at. A test purchase costs the unit and the analyst's hours to inspect and trace it, so the budget covers far fewer parcels than there are sellers on the list. A fair amount of time goes into ghosts, such as a low price that lasted two days or an unfamiliar name that never returns.
Price differences between EU markets are what makes cross-border arbitrage possible. In Eurostat’s 2024 price level comparison (Household consumption: price levels in 2024), consumer electronics prices ran from 89% of the EU average in Italy to 115% in Finland. Whether anyone uses the spread depends on logistics and on how your own channel is supplied. The price gap fails to clarify the source of these goods.
Marketplaces are where this plays out. According to the HDE Online-Monitor 2026, produced by IFH Köln for the Handelsverband Deutschland, marketplaces handled 56.7% of German online revenue in 2025, and Amazon’s Marketplace alone accounted for about 46%. A seller-level dataset for Germany is therefore largely a marketplace dataset, and it must refresh often enough to catch sellers who appear and disappear between two checks.
With Online Mind’s Channel Monitoring, you see every seller active on your products across marketplaces and retailer platforms, so you can tell where a test purchase is worth the budget.
Online Mind’s MFLS metric serves as a stock indicator: a seller that holds that position repeatedly has units to sell repeatedly. A seller that shows up across many SKUs and platforms over several weeks probably has stock that keeps coming in.
Four criteria narrow the list:
A seller that appears on one SKU for a few days and then disappears can stay under observation. A seller present on eight SKUs across different marketplaces for six consecutive weeks, carrying a flagship line and missing from the dealer list, is the strongest candidate for a test purchase. That combination points to a recurring source.
Authorization also tells you where to look. A seller already on the dealer list points back to the brand’s own distribution network, while an unlisted seller points to a source outside it. Both are worth knowing, and the unlisted seller usually goes to the front of the queue.
A test purchase answers where an arbitrage seller's units come from. When the parcel arrives, look at the packaging and printed labels, the batch and serial numbers, and country-specific details such as plug type, language, and warranty terms. Check the invoice and selling entity, and whether the serial number is already registered with the warranty system in another market. Then follow the serial number to the shipment it belonged to.
The trace ends in one of four places:
Sometimes the stock traces back to the brand's own distribution network, where a volume bonus or a promotional stock program puts more units into a channel than that channel could sell. This is one of the more common ways brands give away margin. Reviewing the distribution structure is then a strategic decision for the brand based on its own commercial model, volumes, and agreed services. The brand does not set or dictate resale prices, because each seller remains free to set its own prices under EU competition law.
Protecting your brand's value proposition covers what the brand promises: authentic product, a warranty that works, authorized distribution, listings that look the way you approved them, and the margin structure the brand sets for itself. Unauthorized or infringing supply behind an arbitrage seller wears down each of these, even if most of what surfaces on the dashboard is lawful cross-border trade. Finding the source and handling it takes time. It also pays back across many listings at once.
With a live dataset and an AI-supported analysis, the brand sees its own distribution network in detail. That supports internal decision making and future distribution planning. Over time, visibility turns into a distribution strategy that protects a brand’s margin.
This is the strategic partner role we take with brands: providing the data they use to make those decisions and protect what they've built.
Prioritizing arbitrage sellers starts with one question, which seller has a continuing supply of the product, and breadth, persistence, product relevance and authorization answer it. A test purchase then shows where the goods come from, and hourly monitoring supplies the history that makes the ranking possible.
Pricing decisions remain with each seller, as required under EU competition law. Online Mind's monitoring data is used exclusively to inform each brand's own strategy and is never shared with, or used to influence, individual sellers. This is general information, not legal advice.