Like it's been said in a few different ways here , times are different , things have changed , people are leery . I don't even ask anymore . The last time I did a private property was when I was talking my Dogs for a walk and a Lady was in front of her house . She immediately took a liking to my Dogs and she petted them and we talked "Dogs" for quite awhile .
I noticed her front lawn had been turned over for some gardening work and asked if I could come back later and detect it . She said yes and I did . My best find was a 53' Canadian penny , a little bit of clad and a bit of trash .These are the types of situations where I will ask .
I won't criticize anyone for door knocking because I can see where in some situations it works out well .Myself , I'm the kind of guy who likes privacy in my "Castle" ( I hate the hell out of Telemarketers also ) and I don't want to bother other folks in their "Castles" either .
Yes , I may not find as much as some but when I do I greatly appreciate it .