Learn English – What’s the word or phrase to describe this behaviour

By pure luck I came across this term which describes a similar sales technique:
Lowball Technique

An unscrupulous sales technique where customers are initially quoted a lower price, then informed that there has been a mistake and the actual price is higher. Customers who initially agree to pay the lower price are much more likely to continue with the sale at the higher price.

Low-ball

The low-ball is a persuasion and selling technique in which an item or service is offered at a lower price than is actually intended to be charged, after which the price is raised to increase profits.
An explanation for the effect is provided by cognitive dissonance theory. If a person is already enjoying the prospect of an excellent deal and the future benefits of the item or idea, then backing out would create cognitive dissonance, which is prevented by playing down the negative effect of the "extra" costs.

Also, perhaps:
unscrupulous adj. Devoid of scruples; oblivious to or contemptuous of what is right or honorable.

An unscrupulous businessman (for example) is one who will think first and foremost of his own interests and will stop at nothing in order to achieve his aims. In doing so he may employ several tactics which may or may not be legal, but which many would claim are dishonest.

Thus the character's behaviour could be described as being unscrupulous, manipulative and devious.

Some examples from allbusiness.com:

Measures announced to combat unscrupulous landlords
"Local authorities in England are to receive a share of £4 million to tackle rogue landlords, as part of a package of measures announced by the Government to increase the quality of rental properties. The funding, which has been allocated to 23 councils, will help them tackle unscrupulous landlords renting out dangerous, dirty or overcrowded properties."

5 Tips to Avoid Unscrupulous Factoring Companies
"This week I heard a story from an Austin Texas company about the common unscrupulous practice of filing a UCC-1 financing statement against it by a Central Texas based factoring company before they had agreed to do business together."

"looking for a word or phrase to describe the woman/girl who likes pink and frills"

Girlish Adj. 1. girlish - befitting or characteristic of a young girl; "girlish charm"; "a dress too schoolgirlish for office wear"; see The Free dictionary girlish