A polite "no" to free work

Translators aren't the only ones who are often asked to work for free in the hopes of landing a contract. Designers call this "spec" work, and there is now a web site devoted to saying no to this practice. One designer describes how his polite refusal to waste his time on a "free test" actually got him an invitation to work with the company. This sounds familiar. If I approach two translators about taking an unpaid test, and one says "no problem" while the other is simply so loaded with paid work that s/he hasn't got the time for freebies, there are certain conclusions I might draw....