I posted this in another post here but thought I'd add it here too, as it applies just the same!
"Greed" makes people less inclined to accept and or allow you to hunt their property. If they think you might find something worth a lot of money (or gold items) they tend to get $$ in their eyes, say no almost 100% of the time, and or tell you some story about how they are buying a detector to do the property themselves!
I like the "casual" approach where you just walk up and ask if it may be possible to one day come by and do an hr or 2 of scouting around the property for whatever may be buried a few inches in the ground. Act like you've been around the neighborhood off and on for the last few yrs doing various places on a sat or sun here and there, and even though you've not found anything worth any money, you just like to do it as a hobby. Never take your equipment to the door with you as, people tend to be defensive towards strangers, and if they see you standing there with some contraption they've never seen before, and a shovel, and like you're all geared up to start digging holes all over their yard, you're not going to get very far!
Also, talk to them about more than just detecting, and tell them you're really more interested in the history of the area as you've been a part time history buff for most of your life, and like to meet new people & friends to share this passion with as you obtain new places to scout! Never say "I'll split everything with you"! If they ask for some of the finds you make, tell them you're happy to offer anything you find, and you'll stop up to the door at the end of your hunt and offer whatever they want of your finds! Usually- this method will detour them from even asking for/taking anything, and they'll likely say "just go ahead and hunt, but don't leave any holes, etc. and if you find a pot of gold, I want 50%!
It's your approach, demeanor, attitude, how you come off to a land owner, and whether or not you seem sincere in what you're telling him/her as to if or if not they'll let you hunt, and or if they'll want to see everything you find! If you seem nervous, tense, insincere and like you're there just to dig up the yard like a pirate looking for loot, they'll sense it and give you the boot! On the other hand, if you genuinely take interest in them, their history of the town, area, show you're interested in more than just plundering their land, and like to make/meet new people and friends, they'll be a lot more receptive of you and your adventure!