Opticians - guidance on mark-up and valuation please?


I have been approached by a potential client who has the opportunity to purchase an Opticians.  This will be the first time I have experienced this sector and wonder if anyone would have any guidance on the norm for;

     Valuing the business

     Mark-up on cost price percentages

    or Mark-up on cost price plus wages/salaries

Thank you in advance for any help.