If you have a site in mind which has the right amount of staff/footfall it makes financial sense to buy your own machine, a snack machine will set you back about £500 to £1000 average takings of £50 a week profit £25 a week over a year = £1300 with a profit of £300 to £800 less your costs labour/petrol and any machine breakdowns repairs.
If you rent for a year (they try and tie you in for 2 years) your paying £650 in rental and you could have paid for a machine in that time.
The biggest tip is do not purchase a machine thinking you can easily get it sited. Find your site first!
3 year agreements are very hard to get signed even on a free deal plus site finding for big machines is a lot harder. Only way i would say get into big machines is if you are offered a site with 150+ staff in or you will be losing money. You need at leasst 5 machines out with average takings say 50 staff per sweet else you wont be able to rotate stock quick enough as you need to keep about 50 different lines in for snack & crisps.
I agree I have 8 crisps and 4 other snacks including nuts and pork scratchings and then 24 chocolate lines in mine. There are upwards of 250 staff and stock is turning over nicely, any less staff and I would not have the confidence to purchase boxes of chocs and particually crisps which have a 3 month sell by date. Saying that I cant keep up with some lines like crinkly cheddars, pork scrathchings and Yorkies and there is not a dart playing truck driver in the place, buggered if I know where its all going!