Work on fixed installations (faste installationer) has to be done by an autoriseret elinstallatørvirksomhed (authorised electrical firm). Ask whether they hold the authorisation themselves or bring someone who does, and get that on the invoice.
Helsingør and nearby North Zealand towns such as Hørsholm have older coastal houses and apartments near the station. Salt, wind and older roofs show up on roof and facade jobs. The same 4 businesses as the Danish page: ARP-EL v/Morten Petersen, FLYES EL-SERVICE A/S, Lystberg El-teknik ApS, UNI-EL V/LENNART TORBEN SVENSSON.