I notice that tickets from the official site are about $44 but tickets from Passforless and Trip.com are much cheaper. Is there a catch?

Urban Green, sorry for the delay answering.

In regard to Empire State Building tickets for the 86th Floor Observatory (which are $44 on their site):

I took a look at Trip.com and the tickets for the 86th Floor Observatory range from $46.51 for Senior ticket to $48.54 for an Adult ticket. A Child ticket is less at $42.47.

Checking the Passforless site, they do indeed have tickets for the Observatory at lower amounts ranging from $38.40 to $42.90 depending on what day (and time of day) you book. My guess is that they made an arrangement with the Empire State Building to buy tickets in bulk (at a much lower price), which they can then sell to visitors with just enough mark-up to make a profit.

The tickets for the 102nd Floor Observation deck are extra.