Pier One started closing stores, which Shaffer says is the second warning sign that a retailer is in trouble. "If they're taking on more debt and closing stores, that's not a good recipe," Shaffer says. Even if tenants don't post publicly available financial information, there are things landlords can do to monitor their health. "Sometimes, you can find out the store sales from the [local] manager," Shaffer says.

Other signs of trouble are more readily apparent.

Lucky's Market hired construction firms to perform renovations at a lot of its stores in the Tampa area before it ran into problems, according to Shaffer. But the crews stopped showing out for work, which is the third sign a retailer is in trouble, according to Shaffer.

"Back in November and December, the people that were doing the build-outs for these tenants just stop showing up, which is an indication they're not being paid," Shaffer says.

The fourth sign that a retailer is in trouble is turnover, according to Shaffer. For "Employee turnover is high at these companies," Shaffer says. "Some of it [at public companies] is announced."

At a Krystal that CAM was managing in Tampa, Shaffer says he would see three store managers shuttle through during a five-month period. "Part of that is probably the labor market. But if they feel good about growth within the company and staying at that store for the long term, they're not changing jobs every two months," he says. "They went in there, discovered that location would probably be closing and moved on to other things."