I've had the problem of not being able to sell the car for some reason and had the message come up that it's over 50k but I have found a way around it.

As well as selling without the 45 min wait time.

It may not be perfect but this is how I did it.

Things you'll need:
-A friend to do it with (you both gain money)
-A car that you can sell (one that hasn't had cargobob or impound glitch done to it)
-About 200k to begin with

*Make sure you or your friend check that you can sell the car that is going to be duped in the LSC*

*To make fast profit you preferably want the cheetah and up*

How to do it:

1)Person 1 buys a Comet-100k(cheapest super-car that is over the "50K" mark) and places it in their garage where the expensive super-car your going to sell is in for person 2's garage

2)You get person 2 to do the apartment glitch (this is where the rest of the 200k comes in) and duplicate you the car into the slot of the comet.

3)Person 2 sells their car for profit.

4)Person 2 buys the comet for the slot of where the sold car was.

5)Person 1 does the apartment glitch to give car to person 2

6)Person 1 sells car for profit

7)Repeat until your satisfied with profit

As this method requires you to buy a new car for some reason there's not wait time for LSC.

I don't think it matters whether you buy a 10 car garage or an apartment with 10 car garage but for convenience of it being near most things I used apartments (but this costs a bit more money).

This worked for me and my friend. We started with a Cheetah (because the adders were over "50K") but now we've bought a new adder upgraded to do it with making more profit.

Hope if helped and Happy making bare Dollar!