Retail

The Retail feature was added in the 1.7.0 update.

It can sell up to 3 items at any time.

The retail facilities and their tasks

Retail store

It automatically sells your items. A "base amount"(see formula below) is multiplied by the retail store count.

Customer support center

It increases your customer support rating. As a rule of thumb, make 1 customer support center every 5 retail stores, rounded up. (Example: 16 stores is 16/5=3.2 or 4 customer support centers)

HQ

Allows you to control the retail stores. You only need 1 of them, but the game allows more than 1.

Retail selling formula

Not much is known, but testing shows 2 rules.

When the price in store< price sellable to the NPC at (+0.00%)

The demand skyrockets. You can reach 5,000 cars/fac/hr when selling at 15,000(though it's not a great idea).

When the price in store > price sellable to the NPC at (+0.00%)

The demand is:

(demand at (+0.00%) at 1 store)/2^(log 1.25(price in store/ price in NPC selling))*retail stores.

In layman's terms, double the stores give double the output, but only a 25% increase gives half the output.