What are the ramifications of the strange Lashon "Vayusam lefanav Le'echol"?
as Rashi mentions vaguely in Pasuk 55 (See also Ba'al ha'Turim).
Hadar Zekenim - this was in order to keep the ten camels-full of precious things that Eliezer had brought with him from Eretz Kena'an. Alternatively, Besu'el used to have Bi'ah with every girl before her Chupah. He wanted to kill Eliezer, lest people of his city force him to do so to his daughter.
Why did he need to say "I will not eat"? We do not find that they insisted that he eat!
Moshav Zekenim: This shows that it is Derech Eretz to eat when food is put in front of you. They need not tell you to eat.
רש"י: הרי אם משמש בלשון אשר ובלשון כי: כיצד למד מכאן ש'כי' משמעו 'אם'?
גור אריה: מ"עד כי יבא שילה" יש ללמוד ש'אשר' ו'כי' הם לשון אחד, ו"אם" הכתוב כאן הוראתו 'אשר', נמצא ש'אם' משמש בלשון 'אשר' ובלשון 'כי', וממילא גם 'כי' משמש בלשון 'אם'.