Usability:
After verifying an invalid address the info/error text apears in green. It should be red to indicate that there is something wrong, to me some seconds to trigger on the green ("all is right"-looking text)

The droppdown menu/input field for the seller address acts 'weird'. After copying (ctr-v) an address in it sometimes opens up and default selects the old (default) value which gets promptly selected and overrides the wanted (copied) address.

Tried to get it working but stumbled upon some hurdles:
I've got some error messages on start because it couldn't find my username/passwort etc. Found out that preceding spaces (in front of the line) in the bitcoin-qt config file were the source of the error.
Next i got some errors because i forgot to start bitcoint-qt which isn't that much of a problem but, the text in the messages seems strange: "Exception thrown getting block hash: der Wert darf nicht NULL sein. Parametername: value". Shouldn't there a real value instead of the word 'value' be written? Or is the punctuation out of order? Anyway it is kind of confusing.

I also noticed it take quite a while for it to synchronize, it would be helpfull i there would be something like a progressbar to get a sense of how long it takes.

Welcome to the forums

Welcome to the community

it seems to me bitcoin is not only unknown, it also is a hard to understand concept.

is there a collection to compare time/gain ratios?