This study evaluated the use of OASIS, a multi-site exclusion system for gambling halls in the German State of Hesse. It also tested for onsite customer protection at 64 gambling halls in Hesse. Test players displayed problematic gambling behaviour and applied for self-exclusion. They visited the gambling halls again after 14 days. The results showed that most of the OASIS exclusions were self-exclusions made by younger men, particularly those with a migration background. For the test plays, there were no identity checks in 16% of the visits to the gambling halls. Gambling hall staff responded appropriately to problematic gambling behaviour in few cases (7%). During the second visits, test players were able to gamble in 28% of the gambling halls despite their exclusion. The results showed a need for more monitoring of compliance with customer protection measures.