Queries :: How To Activate Query Criteria For Multi-combo Box Via Form

I am trying to make a form where the user can check/uncheck query criteria via several check boxes. The idea is that the user can start with many criteria and then deselect criteria if the search does not return enough results.

I have been setting up several queries and thought I would combine them in a "Master Query", since I thought it may be easier to deal with each criterion and the respective switch this way.

Lets say we run a hairdresser.

I have a field in the form that allows me to select clients. This is also used in the query. Works fine. Now to the hard part.

Example 1:

Each customer has a budget to spend on haircuts.
Each hairdresser offers haircuts from $x to $y.
The query should return all hairdressers that are appropriate for the budget of the selected customer.
There should be a yes/no button on the form to ignore or use this criterion.

Example 2 (this completely threw me off):

Each customer has a set of preferred services from a table (e.g. cutting,washing, coloring).
Each hairdresser offers certain services also based on this table (e.g. cutting,washing, coloring, drying).
The customer and hairdresser table use the services table and a multi combo box to select the services.
The query should return only hairdressers that offer some or none of the services wanted by the client.

Again, there should be a services yes/no button on the form to either ignore or include this criterion.

To clarify, the hard part for me is the query. I am fine with setting up the tables and the form. Just not sure how to implement something like "IF (ServicesCheckBox = -1, 'then use service criterion', 'ignore service criterion')".