1 - It's pretty tell-tale when a "professional" just answers a phone "Hello" and then, worse, won't even identify the company until pressed for several moments on the phone. Are they hiding from bill collectors? Who calls someone, leaves a voicemail, and then when the call is returned they act vague and avoiding identification? Wow.
2 - Extremely full of excuses on their payroll. Every possibly delay excuse under the sun. They get their billing very quickly, then hang on to your cut for another month unless you threaten to escalate the issue to the end-client. Even then, you better have strict records of the hours, because 1 out of every 4 paychecks will initially try to under-pay if you don't notice the error. VERY shady