I'm not sure how Luxembourg works, but in the US the "seller" or landlord in this case pays a fee. Obviously this may be drastically different in Europe, but it's worth having a conversation with an agent/broker.
My wife is a realtor here in TX and when she is in-between home sales she helps people find rent houses and apartments. The seller pays a pre-agreed amount of 30-40% of the first months rent as a type of compensation. The buyer doesn't pay her anything at all. She is incentivized to find the right property for her client so she can get paid, and she also is better positioned to talk to the listing agent/landlord about you and the current competition among applicants. She ends up being able to save people money on application fees that would never get approved.
My wife is a realtor here in TX and when she is in-between home sales she helps people find rent houses and apartments. The seller pays a pre-agreed amount of 30-40% of the first months rent as a type of compensation. The buyer doesn't pay her anything at all. She is incentivized to find the right property for her client so she can get paid, and she also is better positioned to talk to the listing agent/landlord about you and the current competition among applicants. She ends up being able to save people money on application fees that would never get approved.