The parent company's IATA is not the same as the agent having an IATA card. In order to get things like hotel discounts (if they're available, and many times they're not) you have to show YOUR IATA card to the desk. Many places will not accept a CLIA card as proof.
The only real tax advantage is if you actually are a travel agent and you can prove that you're actively in the business of selling travel (ie as a real job) in which case yes you can write off some things. But in general you can do that to offset the income that you earn from being a travel agent.
As for the CLIA card, here's the official info on the card from CLIA:
"Any travel seller or department of a travel seller that is actively engaged in the business of selling cruise travel can be a CLIA agency member if they attest to the fact they are meeting all federal, state, and local ordinances relative to conducting such sales."
Even existing CLIA card holders have to complete training courses in order to renew their cards, so I'd imagine that new cardholders would have to complete courses as well in order for the cards to be valid.
Also note that:
"CLIA has no subsidiary companies or agencies and no outside organization is authorized to solicit or obtain applications for CLIA
travel agency membership or any agency membership benefits program. "
I'd be pretty suspect of anyone other than CLIA just automtically issuing a CLIA card to you.
So even if you get a "CLIA" card from them, the number on it might not be valid. Basically you're looking at a MLM scam.