Dangers of cheap

I liked this post over on PPP at Motley Fool, talking about MUBL (MUBL Group):

When I first invested in MUBL it was cheap. It was cheap because the market they were operating in was seen to be declining and over 80% of their business was with one client. My view at the time was that this risk was more than compensated for by the SP. I thought that the MRW was pretty safe for a few years and the cash that it produced could be invested in bolt on acquisitions which had a longer term future.

The OP isn't the first investor I've read about to have had a bad outcome from investing in a company with only one customer. Take heed.