I think the main difference between 'client' (or customer) and 'patron' is in the way businesses see themselves. When a business thinks people are kind to support the business - that business has 'patrons'. Otherwise people are just customers (to sell or service for revenue/money. Some customers come back often/regularly then they become 'clients'.

For examples: pubs and club and restaurants like to call their supporters 'patrons' - who are known well.

Barbers, butchers, bakeries and lawyers like to call their supporters 'clients' - who are known.

Retail shops and supermarkets just treat mass of people who come into the shop as 'customers' - who buy things.

;-)