Quote 1
WAGNER
Well, sirrah, leave your jesting and take these guilders.
[Gives money.]
ROBIN
Yes, marry, sir, and I thank you too.
WAGNER
So, now thou at to be at an hour's warning whensoever and wheresoever the devil shall fetch thee.
ROBIN
Here, take your guilders; I'll none of 'em.
[Tries to return money.] (1.4.25-30)
This scene occurs just after Faustus has declared his intention to give his soul for Mephistopheles. But unlike Faustus, Robin is not so easily bought. Even though he desperately needs some cash flow, he does not want to belong to Wagner. In a way, even though he's a bit of a doofus, Robin is a lot stronger than Faustus, at least, for now.
Quote 2
WAGNER
I think my master means to die shortly.
He has made his will and given me his wealth:
His house, his goods, and store of golden plate,
Besides two thousand ducats ready coined.
I wonder what he means. (5.1.1-5)
Rich guys like Faustus usually willed their belongings to family members. The fact that Faustus's servant inherits his estate shows just how topsy turvy everything has become since Mephistopheles came around. The little devil told Faustus to avoid marriage, and now here he is, heirless and dying. Well, he made his bed. Now Wagner will get to lie in it.
Quote 3
WAGNER
So, now thou art to be at an hour's warning whensoever and wheresoever the devil shall fetch thee.
ROBIN
Here, take your guilders; I'll none of 'em.
WAGNER
Not I. Thou art pressed. Prepare thyself, for I will presently raise up two devils to carry thee away.—Banio! Belcher! (1.4.28-33)
Robin is not as easily bought as Faustus, who was quick to sign away his soul for the power he believes Mephistopheles can give him. Wagner's use of two devils to frighten Wagner into submission foreshadows Mephistopheles tactics later in the play, when he threatens Faustus with dismemberment by spirits if he renounces his pact with the devil. Even though dismemberment by spirits was always how Faustus's life would end. The moment he signed that contract the deal was sealed.