Unless your lining and prep are faultless most p and d's wouldn't touch your job, so you may as well do it yourself. My tips would be:
Follow the instructions that come with the wallpaper, pay particular care to the amount of time you need to let the paper soak.
Use a 9" short pile paint roller to apply the paste, this will give you a very even covering of paste and you can do it very quickly.
While you're waiting for your paper to soak apply overlap adhesive (it's a strong mix of PVA) at the top and bottom of the walls, around light switches, window reveals etc, this wil prevent peeling.
Use a jointing roller to get your butt joint tight.
Use a snap off bladed knife (and snap off after every 2 or 3 cuts)
A tool called a 'wallwizz' or similar is excellent for smoothing out the paper. It's used in a similar way to paper hanging brush but does a better job
Keep all your tools clean and pick up offcuts as you go.
Good luck