I've done IT freelance for small businesses in my area for 15 years. I've learned over the years that I can tell which small businesses will succeed and which will fail. One thing that I find consistent about the successful companies is how they deal with careless users. If a user is consistently infecting their computer with malware they get fired. The SMB owner sees this as a personnel problem and deals with it. If this user can be so careless with a computer what's to say they won't be careless about their job? (Now, I don't know if it was the malware that got specifically got them fired, for all I know they were too careless about their work which got noticed by management) Multiple $250 repair invoices for one particular user in the span of three months gets probably gets noticed in a smaller company.
Another indicator is how much they invest in hardware and software. There is a sweet spot of sorts, investing too much is careless, investing too little is also careless. When a company won't invest in small things that pay for themselves over the long term, such as the right printer for the right job, they are in trouble. It is also a sign for me to negotiate a higher retainer amount or not add them to my clientele in the first place.