Splinterlands Heron Accounts: What is this business practice?

I used the Heron service and provided 8 accounts of the Heron service with cards.
Since the owner Hive account@felipejoys discontinued the service at the end of the season, I agreed with him that after the end of the season I would buy from him the account for USD 5 each, so that I would not have to undelegate my cards, which would result in a 7-day cooldown.

After Hive account@felipejoys had already sent me the cards from 2 accounts and had given me the price to buy the 2 accounts (in DEC), he suddenly wrote me that he would only take HBD and 5.5 HBD per account (for this one The time was just 1 HBD = 1.03 USD). So it would be $ 4.85 in HBD, but DECs were agreed.

When I did not respond but said that I wanted to pay in DEC as we had agreed to this and as he also wrote in the Discord, he told me that he would not sell to me anymore and posted in the Discord (mind after our chat) the following:

Here is also his statement from May 31st, which he made earlier.

After I wrote something about it, he explicitly confirmed it again:

I really ask myself the question what kind of business is this during an ongoing sales process in which 2 out of 8 accounts have already been sold and it has long been agreed that they will be paid in DEC suddenly change the currency and then want to settle at an extremely bad rate.
He suddenly wanted 5.5 HBD, so the exchange rate he assumed was 1.1 HBD = 1 USD but in fact the market price at that time was 1 HBD = 1.03 USD.

What do you think of such business practices is it normal?

It should be said here that Splinterlands has nothing to do with it, because Hive account@felipejoys offered a service for Splinterlands as own business.