What is the meaning of "Ro'a Yero'a Ki Arev Zar"?
Rashi: The Rasha is shattered, because his heart dared to serve idolatry.
Rashi citing Yevamos 109b: This refers to monetary guarantors [of Shaltziyon. The lender claims immediately from the guarantor. Evil after evil will come upon them!
R. Yonah: If one is a guarantor for a stranger, that he does not know if he is trustworthy, if the stranger cannot or does not want to pay, the Arev will suffer one of two evils. Either the lender will scream at him, and he will be guilty, or Beis Din will force him to pay, and he will properly scream at the borrower. He 'acquires' quarrels and a loss of money [in the latter case], and he turned out to be Ra - he paid after Beis Din forced him. A good Arev resolves to pay the lender immediately if the borrower cannot.
Malbim: Even though a lover must help his beloved whenever he can (17:17), including to be an Arev for him, he should not shake hands, i.e. be an Arev Kablan (the lender may claims immediately from the guarantor). This is Arev Zar - not a simple (normal) Arev. Also for a Re'a (friend), for whom one must be an Arev, one should not shake (be a Kablan), for then he is not secure (he may need to pay first).
What is the meaning of "v'Sonei Soke'im Bote'ach"?
Rashi: They shake hands to do evil and go in their counsel.
R. Yonah: A good person who hates quarrels will avoid Arvus for a stranger; only he can trust in his wealth. If he does not hate quarrels, he can stumble in this when asked [to be an Arev] - "v'Lashon Rachah Tishbar Garem" (25:15).
Malbim: Refer to 11:15:1:4.
