Audio Classics warrants used equipment for at least 6 months; probably similar for Tom Manley.
To suggest that equipment is repaired in such a way so as not to fail for x days is not only unfair, it's just plain untrue. Unless someone has a crystal ball, nobody can possibly know if & when something will go wrong - which is always a possibility despite the best preventative efforts.
The point is that the buyer's chances are far better when purchasing from trusted & reputable seller than the unknown private seller who in most cases has no way of knowing whether a unit is performing to spec. Also, the dealer's experience can go a long way in knowing where attention is most often needed with a given model.
Cheaper does not necessarily equate to a better deal. Oftentimes, it's exactly the opposite, in my experience - for whatever it may be worth.