[SalesForce] Pass parameters from URL to SOQL query.

Solution to your question could be a dynamic query. So instead of making a query inside a for loop (this is actually not a good practice because it will take more time and you can easily hit SOQL query limit, what is more in each iteration you're currently quering for the same thing) you could just add in each iteration a pair of conditions. So my suggestion is to do it like this:

if (meterIdsToInsert.isEmpty()) {
    // Do something when map is empty
}

String queryString = 'SELECT Id FROM Quote__c ';
String whereCondition;

for (Id meters : meterIdsToInsert.keySet()){
    if (whereCondition == null) {
        whereCondition = 'WHERE ';
    } else {
        whereCondition += ' OR ';
    }
    whereCondition += '(all_products__c  = \'' + meters + '\' AND supplier__c = \'' + meterIdsToInsert.get(meters) + '\')';
}

oldQuotes = Database.query(queryString + whereCondition);

So this should produce a query String like this (for your example map)

SELECT Id FROM Quote__c
WHERE (all_products__c='1' AND supplier__c='a')
    OR (all_products__c='2' AND supplier__c='a')
    OR (all_products__c='3' AND supplier__c='b')

When passing parameters in a URL, you can grab the parameter values in your Visualforce Controller by using:

String thecaseID = System.currentPageReference().getParameters().get('caseID');