Our conduct has made him afraid that American engineers can't be bought.
Evidently he must have his report signed by American engineers of repute, which means that he is trying to sell his worthless mine to Americans.

Harry, we're teaching Don Luis to respect the honesty of American engineers; we're saving some of our countrymen from being swindled, probably out of thousands of dollars; we're proving that the American engineer is honest, and we're discouraging rascals everywhere from employing us in crooked work.

Now, honestly, isn't all that ambition enough to hold us for a few weeks ?" "I suppose so," Harry agreed.

"But what is the end of all this to be.

Won't Don Luis merely have us assassinated in the end, if we go on proving stubborn ?" "He may," Tom answered, pressing his lips grimly.