You’ve applied for a shift which has been published by the client. Everything that was mentioned in the description has been agreed upon in the commission contract. If you’ve been hired as a ‘barista’ for your shift, the client can’t put you in the kitchen to go and clean the dishes if this was not previously mentioned in the shift.
The client can always consult with you, whether you would like to perform other jobs. It’s up to you whether you agree with this or tell them that this is not what you agreed upon in the contract. You can give them feedback that they should add this to the shift description beforehand so that a freelancer knows what to expect.
Please note: When you agree to perform other jobs, your performance in these jobs will be taken into account when they give you your eventual rating.