it's pretty much always higher on separate materials...the issue sometimes is the amount of LABOR involved to separate...sometimes it doesn't make sense.
As far as negotiations....don't worry about their profit margin, all you have to worry about it yours. WHAT can you pay and still make the margin you want/need to in order to make buying, transporting or whatever the item in question....ie I don't break down certain
ewaste because I have set my hourly rate at like $50/hr and NO WAY I can get that doing certain things...know your number and then start low, see WHAT they say, if they blow you off, tell them to come back with a number...NOW you have info, if it is CLOSE to your number then you can probably just say...look I can't pay that, but I CAN pay X. If it is lower than your top number, then congrats, you already won...but don't just say yes, try to get a bit off. If the number is REALLY high, then just say... WOW...that's quite a bit...who in the heck pays that? I NEED THEIR NUMBER! LOL.....some will try to shoot for the moon. Tell them there is no way you can do that number and say how about this (go in about 80% of your top)....if they balk, say "look, heres the deal...this is the final amount I can pay, that should save us some time....I can do $X, not a penny more....what do you think?" If they still say too low, then you did your best, thank them and tell them other stuff you buy if they don't buy it (say ewaste) and then walk...
I have done sales for over 20 years....this is the way the game is played.
Good luck!
Bookmarks