Word to describe the caring of the seller for the buyer?

A buyer and a seller come to a trade agreement. During the discussion, the seller (whose product is good quality) shows that they are a generous person, like so:

The buyer expresses that although they can handle the original price, a little discount for each product would make the total more affordable. The seller agrees to a discount.
The buyer requests that due to the time it takes for delivery, the products be sent at once. However, the buyer says that the money can't be sent at once because, even though a discount has been agreed, the sum total is still large. The buyer requests instead that the money be transferred in monthly installments. The seller agrees to both of these requests.
Eventually however, despite the seller having accepted all the requests of the buyer, it transpires that the buyer has to buy an alternative product from a different seller. The seller understands the situation and kindly allows the buyer to cease the transaction without incurring any costs, penalties or obligations.

Thanks to this generous conduct, the buyer wants to thank the seller. What would be an appropriate term to use in these circumstances?

Thank you so much for your _______

I know that kindness, caring or help would fit, but I want to find a more specific word or phrase.

The seller has been very considerate; he has shown considerateness or consideration.

considerate
adjective con·sid·er·ate \kən-ˈsi-d(ə-)rət\
: thinking about the rights and feelings of other people : showing kindness toward other people [m-w.com]

consideration
noun con·sid·er·ation \kən-ˌsi-də-ˈrā-shən\
: careful thought : the act of thinking carefully about something you will make a decision about

: a desire to avoid doing something that will make another person sad, upset, angry, etc. [m-w.com]

As @talmu pointed out in a comment, it would be more acceptable/idiomatic for the given situation to say something like "Thank you for being so considerate."

You're correct that kindness, caring, and help are the wrong words to use in a business context most of the time. Businesses are not in business to help the needy, they're there to make money. Also don't use a word like generosity that might prompt the seller to reconsider whether they're giving up too much in the deal. I would suggest a word such as flexibility.

I’d suggest using understanding (= a willingness to understand people's behavior and forgive them), either alone or perhaps with the bracketed language below:

Thank you for your [continuous] understanding [throughout this process].

(Merriam-Webster)

customer service (noun):

the way that an organisation deals with customers, before, during, and after a sale, and the activities involved in dealing with customers

'The mobile operator has a reputation for outstanding customer service.'

Source: Cambridge Business English Dictionary

the assistance and advice provided by a company to those people who buy or use its products or services

'A recent survey on customer service concluded that nine out of ten customers say how they are treated by a business is a major factor in determining where they will buy.'

Source: ODO

Suggested phrasing of OP's sentence: