Corrected entry: After Charlie finds the last ticket, "Slugworth" stops him to make an offer. As he talks, he mentions a better home, good food and comfort for the family. It wouldn't be possible for him to know Charlie's entire situation in the couple of minutes since the ticket was found.
Movie Nut
9th Dec 2015
Correction: As Willy Wonka tells Charlie near the end of he movie, "Slugworth" is really Mr. Wilkinson who works for Wonka. By no coincidence does Slugworth/Wilkinson shows up whenever a Golden Ticket is found, it is possible Wilkinson planted them to get the appropriate mix of children (spoiled rich, gluttonous, poor, etc.) Wonka would want to test to see who is worthy to inherit his factory. Slugworth would no doubt have cash on hand (provided by Wonka) to tempt a poor child with money to get the secret of the Everlasting Gobstoppers to test the child's reliability.
Scott215