I have made a simple guide on how to only get top range vehicles on sourcing missions. Ideal for solo CEO's, source, sell, source, sell etcetera. Making your profits really worth it.
Basically, you complete the collections (takes some time, I know) and sell the top collection, bottom collection or both. After this you will only be given top range vehicles on sourcing missions. When either of the collections is completed again sell that collection or don't complete them at all if you want to do Import/Export gameplay 100% solo.