There are two fundamentally different reasons merchants will give cash discounts.
One is that they will not have to pay interchange fees on cash (or pay much lower fees on no-reward debit cards). Gas stations in my home state of NJ already universally offer different cash and credit prices. Costco will not even take Visa and MasterCard credit cards (debit only) for this reason.
The second reason, not often talked about but widely known amongst smaller merchants, is that they can fail to declare the sale (or claim a smaller portion of the sale) to the authorities in order to reduce their tax liability. Obviously the larger stores will not risk their jobs for this, but smaller owner-operated ("mom and pop") stores often will. This applies to both reduced sales tax liability and income tax liability. This used to be more limited per sale (but more widespread overall), since tax authorities would look closely for a mismatch between declared income and spending, but with an ever-larger proportion of customers paying by credit card, merchants can take a bigger chunk of their cash sales off the books without drawing too much suspicion.
Both of the above are more applicable to TVs than cars, since (1) car salesmen make substantial money from offering financing and (2) all cars must be registered with the state, so alternative records of sales abound. Also, car prices tend to be at or near the credit limit of most cards, so it is not as common to pay for them in this way.