Can anyone confirm if what a Qantas Customer Service rep is true?

Can anyone confirm if what a Qantas Customer Service rep is true? I'm travelling from MEL to SIN in December, and want to link my booking to my Jetstar Asia flight to BKK. I have a 2 hour connection time and she (rather curtly) told me I would have to collect bags in Singapore and check in separately for my flight to BKK. When I questioned that they had an interline agreement she said it didn't matter. I find this hard to believe both being under the Qantas group, etc.

The Qantas agent is correct.  In your scenario, Jetstar will not transfer your baggage.  Read the baggage transfers policy on the Jetstar web site.

Yes the Qantas agent is correct. Interlining only works if you purchased a through (and more expensive) ticket with Qantas. Seperate tickets booked with Jetstar Asia for onward travel from SIN would require you to clear immigration and customs and check in at the Jetstar counter at SIN T1.

2h is a bit tight. If I were you, I'd write off that Jetstar flight and purchase a new and later flight.

Alternatively, and to illustrate the difference and benefits of the OW framework, you could purchase a MH SIN/KUL/BKK ticket. QF would be able to interline you on your MH flight on the basis of OW interlining rules. Jetstar is not part of OW so passengers cannot benefit from OW interlining rules.

The flip side however is that if you're only Qantas Club member and were flying Economy, you can't use the lounge in SIN prior to your MH flight. Nor can you use the QF lounge because your QC access rules do not include onward flights with other OW carriers (except AA, but that's a different matter).

It's fun and games!

If you do stay with your jetstar flight I would suggest clearing immigration in Singapore and re checking your bag that way rather than using the transfer desk. I've used it twice coming off QF to jetstar Asia and had my bags lost twice, so 100% fail rate for me.

I don't see why they won't

I've done the following transfers

QF Dom -> JQ Int

QF Int -> JQ Int 

QF Int -> JQ Asia Flight

on seperate bookings and its worked several times

It is possible to do in their system its depdent if they want to do it or not at check in 

I am sure that technically they can. I am not sure though that they willing to do it. I have separate booking MEL-BKK by JQ (though QF ticket) and BKK-HEL with AY. When I came to airport they said that it is “absolutely impossible” to transfer baggage in BKK. Then I pointed that my ticket actually QF one and as such they have to. She did something in computer and said “Still impossible because BKK does not allow for bags to stay overnight in airport”. Then I said that it would be true if my layover more then 20 hr (it was not). She replied “They have special rules and it is impossible”

I came to other counter and asked the same question. And answer was “Yep, no problem. Only things that you have to do is to show baggage tickets when you will register in BKK.” Sure everything worked.

Morale: ask politely and if rejected ask someone else. Works for me each and every time.