Great products make great sales, and great sales make great products. I need two examples for both questions for discussing each response.

This post is not clear as to what the question actually is. I think it is asking for examples that help explain those two statements about products and sales.
"Great products make great sales" is emphasizing a company's choice to make high quality products in order to encourage sales. Basically, a product that the public views as long-lasting will be purchased because it is far and away better than other products out there. The car industry is a good place to start looking. Cars that repeatedly score well according to Consumer Reports or Motor Trend are cars that consistently sell well. People recognize that cars from Toyota and Honda are among the highest scoring cars in terms of safety, options, and overall value. These cars sell well because they are a quality product.
The food industry also can provide an example of great products making great sales. The hamburger chain Five Guys Burgers and Fries has been around since 1986, and by 2003, the company had more than 1,000 locations spread across 47 states and 6 Canadian provinces. They have been approved by ZAGAT every year since 2001 and repeatedly beat out other franchises for "best burger." They make a high quality product, and that quality is reflected in the sales.
The statement "great sales make great products" is similar to the first statement, but product quality is not necessarily paramount. This statement is emphasizing the effectiveness of consumers getting on the "bandwagon." Black Friday sales are a good example of this. A company can introduce a product or sell a current product at a steeply discounted rate. Consumers will purchase it simply because it is a low-cost and low-risk purchase. That product may then attain a "great product" status simply because a lot of people purchased it. The product might not be of the best quality, but it is a great product in terms of the company's bottom dollar. If it made the company a ton of money, then it is a good product. Additionally, if a company can advertise that "x" number of people have and use the product, then other people can be swayed to have confidence in that product as well. As the user base grows, confidence in the product grows as well, and the formerly middle-of-the-road product choice becomes a viable top-tier choice. This is what Android and Samsung did in order to put a major dent in Apple's cell phone sales. Samsung came along and offered a product that was debatably worse (up to opinion) than Apple, but the price was initially lower. Now, for the most part, the Samsung Galaxy products are considered some of the highest quality products in the cell phone market.
https://www.fiveguys.com/-/media/Public-Site/Files/mediafactsheet123016.ashx?la=en