I don't have experience with COVID testing but I'd ask about their disposable PPE supply (gloves and masks), general PPE approach, and worker organization system (e.g. strict work shifts). Based on their responses, would you believe you'll be physically separate from potentially aerosolized samples at all times, for example by using disposable gloves and sleeves/lab coats that you immediately remove after handling open samples, having access to masks & goggles (possible overkill, given that samples should be sealed outside of biosafety cabinets), having reliable biowaste streams/practices, and knowing that the place wouldn't be overstaffed? You could ask current/past workers about general safety culture as well. I'd be concerned if they've had to lower their PPE standards due to shortages or failed to implement good social distancing protocols. That said, having worked with food pathogens, I was surprised how easily safety is covered by standard BSL practices (which often overlap with practices to prevent contamination for non-pathogenic biological materials.) You can also try to base some questions off general BSL-2 practices.