Ag is making a profit (albeit a small one) - you have forgotten about the VAT. As a business, you would be registered for VAT so you would claim back the input VAT (the tax your supplier charged you) but you would have to add VAT to the sales price and send the difference off to HMRC. So, if you get charged £100 in VAT and later charge your customer £110 VAT when selling those goods, you send HMRC £10 and that is all it has cost you in VAT - not the £100 you paid your supplier in the first place. That is massively simplified as: (a) VAT is complicated and (b) I only know the massively simplified version! I am not an accountant - I accept no responsibility for knocks on the door at 7am followed by four HMRC heavies shoving past you with a search warrant
).
If you are not registered for VAT (earn under the threshold - whatever that is now) you will pay the VAT to your supplier but will not charge VAT to your customer and so cannot claim anything back.
Anyway, selling film is the wrong business - the markup on Winchester bottles is about 150-200%... I just bought 12 x 1litre amber bottles incl coned caps from a lab supply company for £3 each (inc carriage & VAT!) - have a look-see what some of the photo shops are charging
