Wholesale Supply Side means 'parties' under the Four-Party Schemes and Three-Party Schemes except Credit Cardholders, together with the particular Credit Card Payment Scheme. 

All 'parties' except Australia's 7,515,000 circa Credit Cardholders (aged 18 or over) as at June 2016 have powerful lobby groups to Argy Bargy reasonably equitable pricing for Merchant Service Fees et al.  So the User Pays Principle would more naturally prevail.

See:

Retail Supply Side.

RBA's Reform of Credit Card Schemes in Australia: "A Consultation Document" – December 2001