Is quickbitcoins.net reputable? Mailed in cash with postal envelope. Website started acknowledging receipt via postal delivery 3 weeks since. Blockchain within 3 hours of "caught up". Yet no bitcoins.

Is it a scam?

Cash amount was small, should not pose problem. Was what you call "pilot test" and had bitcoins arrived promptly would be followed with larger purchase.
I used quickbitcoins.net successfully 4 times. They are gone now. The 800 number is disconnected and their e-mail address returns nothing. Try to find the http: website on Explorer or on tor and neither can find it! Site no longer exists! If you send coins to them without checking you will loose your money!