Question about Carvana

Carvana gave me a different quote on buying my used car if it's a trade-in versus just a sell. $11,083 for trade-in, or $10,300 for a sale. So, I'm thinking that there's a shell game going on here. They're going to dictate who is selling and at what price. Right? I already have a dealer in mind that I bought from the last time when they had the lowest price (probably because they're outside of expensive Los Angeles). I can sell my car privately for $12,000. I would take $11,083 if I could buy a new car from the dealer of my choice without being cramped by a middleman (Carvana) raising that sale price.

So, they're giving you $783 more for your car if you buy from them...olain and simple or am I missing something?