If you are hiring an editor and don’t read and do some basic editing yourself, you could be wasting money. While some editors go by word count, others have an hourly rate. If they are spending their time (and your money) editing silly errors, such as the missing words (or wrong word – their/they’re/there), you may as well throw your money out the window. Get better bang for your buck. Also, if you are not editing first, you are not presenting your best effort. I think it makes the writer look a tad unprofessional. If you don’t care enough about your work to try to make it the best you can, why should anyone else care about it?