[v3d4]

1. i dont know. if youre worried this guy is the type to give you the highland business then i suggest buying a small amount or set your own limit by deciding how much you want to pay, and just tell him you can only spend 20 pounds or whatever. dont give a number higher than youre willing to part with. if he tries to offer you some tiny little amount for that or tries to talk you out of more cash just say no thanx.

2. the only way to judge quality by looking comes from experience, as far a i know there is no other way. its very difficult to tell just by looking, because theres some fantastic looking stuff out there that is really very weak, or hasnt been handled properly and will have a bad taste, etc.
while the only true test is in the smoking, the three things to note are look, smell and feel. all three things taken together can give a rough estimate of quality. avoid a lot of thick stems and twigs or anything which looks leafy. look for reddish/brown pistils, sprinkling of crystal frosting (which will not be apparent in all cases) and a pleasing green color. if it looks brown or ugly, thats not necessarily a sign of bad weed if the smell and feel is good. if it has a funny smell (like ammonia for example) it should be avoided. you want a good smell, not necessarily strong, but simply that good weed smell. if you dont know tht good weed smell then youll know it when and if you smell it.
the feel of weed is variable so i dont know what to say beyond the obvious: it should be neither wet and mushy nor crumbly powdery dry; neither hard and crunchy nor excessively light and fluffy.
edit: hard and crunchy may be ok but not too hard and crunchy, like it was dried in a kiln

usually cool people will let you have a little toke before you buy any. if they dont/wont or circumstances dont permit, then you should only buy a small amount like a gram or two. if they wont go along with that, and say stuff like "i only move weight, i dont have time for nickel and dime bullshit" (or whatever your UK equivalent is) then you should not do any business with them.

3. when the time is right, the perfect safe and secure smoking place will present itself. if the perfect place does not manifest, then the time is not right.

hope this was helpful.
you should also search these forums and will probably get much better answers and way more info that i have given here. good luck