Sometimes it is a warning. More often it is an opportunity, because most buyers assume the worst and stop looking.
Buyers see "back on market" and assume the inspection found something dreadful. Sometimes. Frequently not. The real distribution looks more like this:
Only two of those are about the property, and one of those two is often negotiable rather than fatal.
Ask. Your REALTOR® can contact the listing agent directly and ask why the previous deal did not complete, and in most cases will get a straight answer — listing agents generally want to head off the same problem twice.
Additionally, a REALTOR® can see the property's full listing history: previous list prices, how long each listing ran, when it went conditional and when it returned. That pattern is informative on its own. What a REALTOR® can see →
If an inspection was the cause, ask whether the seller has the report or has since done the work. Sellers who have fixed the issue usually want you to know.
A seller whose deal has just collapsed is in a materially different position from one who has just listed. They have already mentally moved, they may have committed to a purchase of their own, and they have lost weeks. They are also newly aware that a buyer who can actually complete is worth something.
Meanwhile the buyer pool has thinned, because a good number of buyers see "back on market" and move on without asking why.
Some of the best purchases we have negotiated for clients were homes that had come back on the market for reasons that had nothing to do with the house. The question is never whether a deal collapsed — it is why.
Do your own inspection regardless of what the previous buyer found. Ask for any existing report but treat it as background rather than a substitute. If the collapse was financing, make sure yours is genuinely solid before you write. And if the seller will not say why, treat that reluctance as information in itself.