Beware of the finance

Where do I start? We made and enquiry to price double glazing for the whole house (8 windows). We had a sales man at the door 2 hours after making our initial call. The sales man made himself quite at home and proceeded to stay for 3 hours convincing us that his windows where the best in the market! We ended up singing a contract at 11pm just so he would leave. The windows where seriously overpriced at £9000, the average uk home is around £5000-£6000 however the real shock came when we read further into the paper work of the finance. At no point did the sales man mention that interest rate they provide would have meant that infact the windows would have cost closer to £18000. This is false advertising and very concerning that this company are trying to pull the wool over people's eyes with regards to what form of financial commitment they are actually getting you to sign and agree too! There was also all the usual jargon and pantomime of them calling there manager to get a better price. I would avoid at all cost and I defiantly will be making the financial conduct athority aware of their underhanded tactics that could potentially place people into financial difficultys!