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This shop Alza basically refunds PEB even if the item is above 100g.
The heaviest item I did was about 700g and kinda cheap but someone told me a limit is 1200eur.
The only thing you need to do is sing a declaration on oath (excuse me if I used the wrong term I am translating word for word here)

Anyone can explain why do they refund items right away without cross checking ?
Also is there a chance they check back on all the refs on my accounts and see that weights match ?

If it's something like an affidavit they can take legal action on you if they were to go back and see that you lied about the weights. However, that is incredibly unlikely.