I think that is an excellent idea, a simple non valuable item first to test the results.....and also would it not be acceptable to ask to see samples of their work first !!!! and ask how many years they have been doing this ( 3 months vs 3 years) and how about ask for a list of clients you could call to ask about the quality of their work......
We can all think of what we could have... should have done....but this also should be a good learning curve for us to use in the future.....