This is a natural tactic for almost anyone to use in any situation. We all like to be liked, and will use rapport-building skills such as humour and body language to convey that not only do we like another person, but that we are eminently likeable ourselves.
It also follows the human tendency to like other people who are like us, people that we see as being in the same image as us.
A jeweller might use humour to build rapport and also find out similarities between you and him/her. They may also mimic your body language so as to make you feel relaxed in their company.
The way to combat this tactic is to note to yourself when you are feeling an unnatural liking for the jeweller. There are just too many different ways of inducing liking in another person to be able to stay aware of all of them, so it is best to realise when one or more of those means has worked, and then do the following.
You must mentally disconnect the diamond from the jeweller. They are not the same thing. Your fiancée will be wearing the diamond, not the jeweller. It is possible to be completely agreeable and polite to the jeweller and then not accept his/her deal and walk away. Stay focused on the diamond and the deal at hand, not on the jeweller themselves.
