One may not eat meat or chicken during the Nine Days. A
restaurateur may nevertheless continue to serve meat to those
who wish it because of the possibility that refusal to serve meat
would cause customers to patronize another restaurant. Also, the
food itself is permitted – it is only one of the day’s characteristics
that forbids it, so one may be lenient. (Yechave Daas 3:38)>>>>>>
Adopted from the shiurim of Ha Rav Leible Sternberg