Either because they do not yield thee that satisfaction which thou didst expect from them, but rather load thee with ill humours, and the seeds of divers diseases; or because they are not provided for thee with sincerity and good will, but with some evil design upon thee, either to discover and betray thee, or to enslave thee. See Poole on "Proverbs 23:6,7".
Related Commentaries of Proverbs 23:3
Proverbs 23:3
3 Be not desirous of his dainties: for they are deceitful meat.