If the DirecTV intaller brings the equipment to you, s/he will do the installation. You won't have a choice.
If you want to do a self install, or hire a 3rd party installer, you need to obtain the equipment on your own, from any of several sources. The dish will almost certainly have to purchased on-line (solid signal, value electronics, etc.). Receivers and DVRs may be able to be obtained locally, or on-line.
With the equipment sitting in your house, your independent installer shows up and does all the work.
End result, you will pay more (much more), first you have to buy the dish and second, the installation labor.
My suggestion is to let the installer come and do the work. What you read in forums are the bad experiences. There are lots of good installers out there and the odds are you will get a good one. When he arrives, first thing to do is walk through the entire installation with him. Make sure you both know, and agree, on exactly what will, and what will not, be done as well as how it will be done. Then monitor the work as it is done, but don't get in the way. Offer to help if it is obvious help would be benevicial. Have a bottle of cold water and/or a soft drink available. If the installer does a great job, consider a gratuity (totally optional).
If it becomes obvious the installer won't be able to do the job to your satisfaction, cancel the job and send him away (he will take the equipment with him).