Clarify the terminology
A voluntary tip is different from a bonus calculated under an agreement. Ask how both are handled and whether there are sharing arrangements. Keep these separate from the fixed amount when comparing offers, and establish whether any quoted figures are gross or net.
Check the records
If a bonus is linked to drinks, learn how it is recorded and how you can review the totals. Ask when it is paid and who addresses mistakes. Avoid projecting one unusually busy shift across an entire month; variable income can change for reasons unrelated to your work.
Keep the boundaries intact
Being reliable and attentive can help the working relationship, but it does not ensure tips. You should not accept unwanted behaviour or drink alcohol to chase an incentive. Raise pressure or unclear rules with the supervisor instead of treating personal discomfort as a necessary cost of earning.