You are too brave for your own good Missy.
A lot of it is in how you approach the dog ( or they approach you, whichever ).... Typically it's pretty easy to tell if they are going to be friendly or not. Even dogs that are barking at you for being too close to "their" property, often change their tune when you talk to them and show them you aren't a
threat.
I had one... a big gray grate dane ( I mean one that his head would be over the 6' stockade fence he'd stand up on big ) that was in the backyard I was needing to get into in order to test for some telephone wire problems. I'd already visited the phone pedestals on either side ( they are placed in every other yard typically ) and the problems was certainly somewhere between. So I went to the house, knocked on the door as always and no one was home ( also typical since it was a work day )... I went up to the gate and did the typical rattling the gate thing and calling for the dog I knew was there... nothing, the dog didn't come to check what was going on. So I went on in... when I got around the corner of the house and saw the dog... I just started talking to him... he just watched me, didn't even bark. I went ahead and did my thing, tested the lines etc ( probably fixed something )... and left.
At the end of the day, went back into the office with the other techs and we were all going over the stuff we'd found and fixed so everyone would be up to speed on the possible trouble areas etc. I went over what I did and one of the guys mentioned the dane up in that area and how "bad" he was... Then I said this was that yard I was in... that the dog didn't do anything ( which is strange, they do usually do at least want attention if they aren't trying to get you )... They couldn't believe it... I'm not sure if they had even tried to approach him before, or if they'd just acted too scare which the dog had sensed... again, the point is that a lot of it is how you approach them.
BTW... I've also met a bunch of dogs that I'd never try that with, some are just too wound up to even try to approach.