If your bookkeeper is in-house then one can always check their emotional quotient by asking them situational questions and checking their response time towards the work assigned.
With outsourced bookkeeping services, always check their customer support and work updating process on what’s late and what is coming up. Analyze their hourly rates and the work completions in it. Ask if they provide their office tour to check facilities and meet their staff.
Ask if the bookkeeper is proficient in the software you want them to use. You don’t want someone who still works on excel spreadsheets.(Also make note of who would hold the account credentials for the software, it is generally advisable for the company itself to own them).Checking how they review their own work will also show consistency and unbiased working ethics.
With that, asking some technical questions regarding the scope of work you expect should also be tested, in fields like bank reconciliations, bill handling procedures, cash flow forecasting, etc.
Since you are providing a person or a bookkeeping business with your company’s sensitive data, you need to make sure that they have proper internal review procedure and quality control. One needs to question about how do they segregate duties i.e. having multiple people with different responsibilities to make sure there is transparency.
With all that said, a standard guideline with the mentioned points in mind should be used to asses every candidate. It helps in prioritizing yournecessities while making decisions.