Make sure you have created a proper corporation (Limit personal liability).
Keep your insurance up to date and make sure you are covered properly.
Train your employees to warn customers of the dangers of batteries.(We pass out a warning card to each new customer).
Make sure your surveillance cameras are recording video and audio and the retention is at least several months.
If your insurance company does not answer their phones (Much like Calco), find another one. I wasted 20 emails and 20 phone calls to them before I opened my shop and I could never get in touch with the person that worked with Vapor Shops (Jason I believe). If you can't reach them to become a client, think what it would be like if you needed them to handle a claim.
Since the battery vendors are willing to send free plastic battery cases with each order, make sure every customer has one and that they understand why!
In the end, when litigation begins, everyone from the manufacturer on up will be on the list. Cover your ■■■ at all costs.