I dare to say it is quite suspicious.
Have you succeeded in measuring the degree of “out-of-tunedness” with any digital or mobile tuner?
Tuning melodica (or harmonica or similar instruments) is definitely not easy – and involves scrapping reeds with the file or scalpel – something that you are not expected to do if you have no significant experience (and a number of broken instruments behind).
If you are sure you are blowing it properly and the sound is too much out of tune – probably you’ve got something which the seller did not want to sell you (if it is a shop, not a person) and you should try to get in contact.