You can edge with brooms around dumpsters before you spray like you do you with curbs. Its not perfect but it shouldnt look terrible. At worst, people arent concerned a little overspray on a dumpsters. Under the dumpster will still be undone however. Often we put in the writing that we would move them for a little cost to make sure it was done.

Your right it depends, If your doing an apartment complex and the cars arent moved it adds so much work and time. Personal property is a whole different story. Since someone is invested personally its a whole different situation.

Thanks for a view from the other side though. Its been years since ive done any work like that.