It's not really repeat nature. It's the same account, but it's for a short period of time each year which would seem suspicious to me, when they claim it's a conference they say the following:

"4/ Our bank statements are none of your business. 5/ The details of our venue agreement and insurance are also none of your business."

So they're refusing to prove it's a conference but requesting that Paypal are "reasonable"? Having your account verified once and then go dormant in payment receipt for the majority of the year then start again would seem suspicious to me... especially when their justification isn't something they're willing to prove.