There should be no reason why you should not apply the GTechniq product yourself but here are a few tips that should give a a good outcome / finish.
1. Preparation - coatings like this will not adhere correctly or give a good finish unless the paint is prepared to exacting standards. There can be no trace of any other wax on the paint, be it synthetic or pure carnauba before application. Plus as these coatings add around 1 to 2 microns on the paint thickness, any scratches, swirls or other paint defects need to be removed prior to application.
I allways carry out a full paint decontamination and at least a 2 stage paint correction / machine polish before application, otherwise you are simply wasting the clients money.
Rush this stage at your peril!
2. Enviroment - the car needs to be indoors, with a constant warm stable enviroment. Most detailers will apply C1 then C2 over the top for example. The C1 should be left for at least 12 hours before the C2 can be applied.
Therfore you do not want the garage going freezing cold overnight.
3. Correct application - GTechniq can, if not applied correctly, ie rushed, use too much, etc, cause streaking to the paint finish. This is more noticable on darker coloured metallics paints. You really do have to concentrate when applying this product, making sure the surface is evenly coated, do not try and cover large areas at any one time. The Gtechniq home tutorial video is very good and helpfull.
Once this " streaking " happens you may have to machine polish the whole panel again to remove it. I would strongly recommend practicing first on an old car panel, you will then see how it reacts when applied.
Rush this stage at your peril!.
4. Most of these ceramic coatings are suspended in a kind of alcohol based solution, thats why you have to wear gloves. C1 tends to " flash off " very quickly when applied, so you have to know its working limits before you have to stop and buff it off, try and be clever here and again it will turn out a mess!
If you are not prepared to be patient and carry out the necessary steps then leave well alone in my opinion.