Undercutting is the most common rule sellers configure, and the one nobody sets a limit on. Here's the actual math, and why the limit matters more than the rule.
If you set up any kind of repricing rule, the first one you'll reach for is "beat the lowest listing." It's the obvious rule. It's also the one most likely to quietly wreck your margin if you don't put a number on "how much."
Most sellers never do. They set "undercut by 1%" or "undercut by $0.05" once, move on, and never revisit it. Six months later half their inventory is priced against a race they didn't notice they were running.
An undercutting rule takes some reference price — usually TCG Low, sometimes market average, sometimes a specific market position — and prices your listing some fixed distance below it. The reference matters as much as the offset. CardTrader's Autopricer tool is a useful example of how granular this can get: it lets a seller target the lowest price, the market average, or a specific ranked position in the listing order, with either a percentage or a fixed-amount modifier, and it can vary the rule by condition and by language. That's the shape a real undercutting rule takes once you move past "always beat the cheapest listing by a nickel."
The point isn't that you need that level of configuration on day one. It's that "undercut" is not one setting, it's at least three decisions: which price you're undercutting, by how much, and whether that amount changes with the price of the card.
This is the part most rules get wrong, because they use one offset for every card in the store.
A flat 5-cent undercut does nothing on a $200 card. Nobody notices a nickel on a $200 purchase, and you've left yourself no room if two other sellers are running the same rule. A flat 5% undercut does nothing useful on a 50-cent bulk card either — it rounds to a fraction of a cent, TCGplayer's pricing granularity swallows it, and you've achieved nothing but wasted a repricing cycle.
If your rule uses one offset type across your whole store, you're almost certainly over-discounting your cheap cards or under-discounting your expensive ones. Usually both.
Here's the actual failure mode. "Always undercut the lowest listing" has no floor built into it. If someone else is liquidating a collection and drops their price to cost, your rule follows them. Then a third seller's rule follows you. Nobody chose to sell at that price — the rules chose it for everyone, one undercut at a time.
An undercutting rule without a price floor isn't a pricing strategy. It's a race with only one direction, and you don't control when it starts.
This is why undercutting can't be evaluated on its own — it has to be paired with a hard floor that no rule is allowed to cross, and ideally with your actual margin, not your sticker price, as the thing you're protecting. See setting price floors and ceilings and fee-aware, net-margin repricing for how to set that bottom.
It's "what's my floor, and how close to it am I willing to sit."
Undercutting works fine as a component of a pricing strategy. It fails as the entire strategy, because a rule with no bottom will eventually find one for you — usually the worst possible one, set by whoever panicked first. If you're running an undercut rule today and can't say offhand what your floor is on your top movers, that's the gap to close before you touch the offset amount.
At volume, unbounded undercutting is close to always a mistake. It optimizes for winning a single sale today at the cost of the price everyone in the category converges on tomorrow, including you.
Set a floor first, per card or per tier, based on your cost and the margin you actually need. Then let undercutting operate inside that floor, not around it. Use cents-based offsets on your cheap inventory and percentage-based offsets on the rest. Revisit the offset numbers occasionally — a rule set once and forgotten is exactly how a store ends up racing to zero without anyone deciding to.
Hoard's repricing agent applies floors before it applies any undercut, so a rule can't push a listing below the number you set no matter how far the market moves. You can read how the underlying sync works in how Hoard's repricing agent works.
Connect your TCGplayer store and see which listings are already sitting closer to a race to the bottom than you'd choose.
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