This is an obvious point, but making sure that there aren't multiple similar functions in one place is a must.

Over time with multiple deployments, builds and re-designs it can be easy to duplicate functions, like "Contact us" links or buttons.  they could be in the head, the sidebar, in an article and the footer.

They could also all be labelled differently; "contact us", "call us", "our numbers", "get in touch" etc.

If a customer sees something like this and recognises it as fragmented functions they may be less likely to convert as it's overly complex.  If a customer doesn't realise all the functions are the same then they'll spend time trying to differentiate between them, often causing frustration.

Keep it simple and it may worth having a third party review the site for this type of thing as we can become blind to it on our own sites.