Ferrari dealer dont sell car cheap because no sale in 1 week. Expensive things take time for people to collect the funds. Never rush.
You can't collect $50,000 in 7 days, bank deposit takes time, so does selling existing item to fund big purchase.
Be careful not to sell too cheap, the experienced player may try to take advantage of your inexperience. I've made a mistake ingame due to that. Take your time to sell it.