Why does the Pasuk refer to Lavan here as "Lavan ha'Arami"?
Ramban: To teach us that, although he, together with all his townsmen, were tricksters, Hashem appeared to him in honor of Ya'akov. 1
Targum Yonasan: It was not Hashem who appeared to him, but an angel with a sword drawn, who appeared to him in a dream of the night. Presumably, the Pasuk then refers to "Lavan ha'Arami" precisely because he was the swindler that he was, which is why he needed to receive a stern warning to obey orders and to treat Ya'akov with due respect.
What did Hashem mean when he warned Lavan against speaking "from good to bad"?
Rashi: Even if a Rasha wants to do good for a Tzadik, it is bad for Ya'akov. 1
Ramban and Seforno: He warned him not to promise him a reward if he returned with him to Charan, or to threaten to harm him should he refuse.
Bechor Shor: Do not speak bad, i.e. even harsh words of rebuke to benefit him.
See Sifsei Chachamim.
רש"י: כל טובתן של רשעים רעה היא אצל הצדיקים: למה כך הדבר?
מהר"ל (חידושי אגדות, יבמות קג. עמ' קמה ד"ה כל): הרשע הוא הפכו של הצדיק, ולכן לא מסתייע שתבוא טובה מהרשע לצדיק.