Not trustworthy, questionable, or not in line with professional or moral standards.
example
Das Jobangebot per E-Mail wirkte unseriös, da es ein extrem hohes Gehalt für wenig Arbeit versprach.
The job offer by email seemed dubious because it promised an extremely high salary for little work.
Usage tips
Word structure
The adjective 'unseriös' (dubious) consists of the prefix 'un-' and the word 'seriös' (serious/reputable). The prefix 'un-' expresses the opposite. Something that is unseriös is therefore 'not reputable' or not trustworthy.
EXAMPLE
Ich habe die E-Mail gelöscht, weil der Absender unseriös wirkte.
I deleted the email because the sender seemed dubious.
Typical collocations
'Unseriös' (dubious) often describes things in a business or informational context. Common combinations are 'unseriöses Angebot' (dubious offer), 'unseriöse Firma' (dubious company), 'unseriöse Quelle' (dubious source), or 'unseriöse Geschäftspraktiken' (dubious business practices).
EXAMPLE
Vorsicht vor unseriösen Angeboten im Internet, die zu gut klingen, um wahr zu sein.
Beware of dubious offers on the internet that sound too good to be true.
Use with 'wirken'
The adjective is often used with the verb 'wirken' (to seem/appear) to describe a questionable impression. The structure is: 'Etwas/Jemand wirkt unseriös' (something/someone seems dubious).
EXAMPLE
Die Webseite des Anbieters wirkte auf mich sehr unseriös.
The provider's website seemed very dubious to me.
Compare with
antonym
unseriös vs ernsthaft
serious / seriously
'ernsthaft' and 'unseriös' are opposites when it comes to a serious attitude or trustworthy behavior. 'ernsthaft' describes that someone really means something and approaches it responsibly. 'unseriös', on the other hand, describes something that seems dubious or that should not be trusted. 'ernsthaft' can also simply mean 'not joking'. 'unseriös' goes further: it judges a person, an offer, or a behavior as unreliable or unprofessional.
unseriös
Das Reiseangebot im Internet wirkt unseriös, weil wichtige Informationen fehlen.
The travel offer online seems dubious because important information is missing.
ernsthaft
Nach dem Gespräch nimmt die Klasse das Thema ernsthaft.
After the discussion, the class takes the topic seriously.