Legal Question in Personal Injury in Maryland

Recent Maryland appelant cases have held a landlord liable for a tenant's dog biting a visitor to the premesis, so the answer to your question is yes you could be held liable (depending on the fact of the case) and more importantly you may be the only potential defendant with liability insurance

Your solution if you want to help your friend, is to require that he obtain liability insurance with

YOU ADDED AS AN ADDITIONAL INSURED...

Good luck

In addition to the liability insurance suggested by Mr. Laake, consider having a lawyer draft a release for each customer sign and an indemnity agreement for the business owner to sign.