I assume multiple retailer implies delivery to a warehouse, or could you get distributed deliveries included with those discounts ?
A multiple retailer is generally considered to be a retailer with at least 5 shops.
Nothing to do with where the goods are delivered. Multiples tend to have a head office which might include a warehouse. Deliveries might be to a central warehouse from which company distribute stock to each branch. Some suppliers deliver direct to the branch. To minimise capital tied-up in stock, the trend has been towards just-in-time delivery.
Local traders buy stock from the suppliers which could be a wholesaler, direct from manufacturers, trade cash-and-carry. local producers.
The example discounts could apply to any sector.
It's possible for one person to manage up 5 branches (each shop having its own manager and staff). Between 5 and 7 branches, it's challenging for one person but not worthwhile having a team. >7 shops it's usual to have departments for different functions.