In Act 2, what does Sergius mean by "he over-reached us"?

Sergius means that the Swiss fellow charged them too much for the horses. He took advantage of them.

Petkoff. What, that Swiss fellow? Sergius: I’ve often thought of that exchange since. He over-reached us about those horses.

Sergius. Of course he over-reached us. His father was a hotel and livery stable keeper; and he owed his first step to his knowledge of horse-dealing.