If you are trying to create a "RESTful" API, then you should conform to the typical conventions for HTTP methods:
- GET - List/retrieve item or collection (safe to call without changes)
- POST - Create/insert a new entry or collection (will change data)
- PUT - Replace/update an entry or collection (will change data, but can be called multiple times safely)
- DELETE - delete item or collection
So even if you have 50 parameters for your query, use HTTP GET.
For developers using the RESTful style, these are the assumed behaviors-- if they see POST, they will assume you are inserting a record or records.
Wikipedia entry has a little table which you can print and tape on your wall:
https://en.wikipedia.org/wiki/Representational_State_Transfer