That sounds like a pretty poor way of going about business. Despite being a bit sneaky, bare in mind that people who have a live website with hibu will have chosen it to be like that. I used to work there and the customer is involved in the design process and the website is set live once it has received their approval. This might frustrate the designers but ultimately it's down to the customer. Going in saying 'your website is crap' may actually be insulting to them.
I'd agree a lot of the older ones look quite dated but they do end up getting updated for free and the newer ones are mostly decent and competitively priced. I often saw one man outfits/small companies going in for customers like this promising something better, more often than not the results were not what they promised and the customer would be back to hibu. Also note they offer a lot of extra support and just being linked to Yell helps SEO compared to an unknown small company.
If you offer something better then get a showcase of your best work and advertise in the same places. If people are unhappy with what they've got then they'll come to you. No-one's going to trust a cold caller coming in with that pitch..