OK, this is my specialty.
Start out with a massage parlor instead of incall. There are some providers who are certified and have license that are independent that do incall but most of those do not offer extras. There is the rare one that you may find that does offer a handjob. Very rare to find a licensed one in massage parlor or incall that offers extras. So if you want extras, stay away from certified. They do however offer the best massages, usually. Some of the best massages I have had were from unlicensed asian women who gave extras, so you never know...
If it says massage, then it is usually full body. There are massage places that say 'foot massage'. Foot massage only but I have gotten handjobs there. Some places are legit and no 'happy ending'. Most asian massage parlors will give you the handjob at least. Unless they think you are police. Just act relaxed and be yourself and be friendly and 99% of the time, if they do give extras, then you will be offered one. Most of the time if the lady is dressed seductively, you will be offered extras. Usually just handjob but sometimes full service or a BJ.
If I am not offered one, I will politely ask them for one or I will give them a hint by rubbing my dick or playing with my nipples and then see what they have to say about that. If they don't want to give a handjob, don't force it. Just tell them thanks and give a little tip and try another place or girl.
I have gotten erections at strictly legit massages and the girls are always cool. They just tell me to relax and take a deep breath. Nothing to get embarrasssed about. Happens all the time to them and it's a natural response to being touched. Nothing to worry about.
Usually, it's a good idea to be a little bold if you go to a massage parlor. Ask them to see all the girls who are working and you want to take your pick. Be polite as always. These girls just want to be treated with respect and more often than not, they will take good care of you. A cop will most likely not ask to see all the girls to take a pick, so right off the bat they will think you're not police. Good start.
Alot of times if you see an ad for incall massage, those girls will most likely go all the way. Full service, probably blow job with condom on and intercourse. Most of the time their massage skills are nonexistent, so if you want a massage and happy ending, go to a massage parlor. And alot of these incall places will bait and switch, or alot of the time the girl pictured in the ad does not work there at all. It's a crapshoot.
I have had a cop walk in on me while getting massage twice. Just relax and be cool. Nothing they can do as long as you don't have your dick out with a condom on and she has her clothes on. It's pretty rare. I have seen hundreds of girls at massage parlors over the last 10 years and it's only happend twice and with the same girl at the same place.
Good luck, lad. Just be friendly and polite and that will take you a long way.
Edit: the guy above has good points. If it says in their ad 'striclty legit' or nonsexual, don't bother wasting your and their time and asking.
Go to a strictly legit pro first to know what a real massage is, if that's what you want.
As far as being injured, I have never been injured in all my time. It is possible but I have never had any problem whatsoever.