You really want to be able to do as much as possible. And if you can't do it, then it would be in your best interest to have someone that can. Not sure about your area, but although trash-outs are required, if you don't get the initial services and get all that work done and bid the debris - you may not get the trash-out. Also, when in a house for the first time - for many companies you are required to let them know all the issues and bid them or even fix them while on site. Fix a roof leak, replace a sump pump. repair sump pump line, pump out basement, assess mold, etc... Then you will need to make sure you have the allowables covered while on site - change knobs, install lockbox, winterize, cut the grass, trim bushes, trim trees, etc.... The more you can do, the more you can make. The more of a one stop you are, the more work they send your way. You don't have to be completely handy, but you need to look through the allowables and other Preservation items and get a general understanding as to what will be required of you.
Biggest thing to understand - if you go into a house and you are the first time vendor doing the initial services - if you don't report something such as a roof leak or mold or a water stain, etc.... they can come back on you and tell you to cover it at your cost and also cover any extra damage that happens because you didn't fix it or report it.