How to set the default (spawn) property

Online is pretty buggy right now, it's entirely possible that what you experienced is one of these bugs. http://www.computerandvideogames.com/431870/rockstar-working-around-the-clock-to-resolve-gta-v-online-problems-errors-and-bugs/

It's randomness mixed with rank that's about it. The higher level you are, the better the stuff that spawns, but it's still to some point random. So you won't only spawn nice vehicles vs only spawning shit ones

taken from R* forum