In 12 Years a Slave there are a couple of references to Master Ford's debt but it's very vague.
Is it as simple as he owes money to someone? If that's the case then wouldn't Solomon (who's already proved he can make the process more efficient and let's face it - only costs food) be more valuable to him than an overseer who he pays (and by all accounts does a bad job)?
Or is he in debt in some other way (he owes someone his life/a favour?)