I'm flying in from Australia this Saturday. I purchased a 3 entry tourist visa which gives me essentially 6 months in Thailand, with 2 border crossings.
Because I am traveling long-term, and debating about continuing on to another country afterwards, I have no desire to buy a return ticket as yet, since I don't know where/when I will be leaving from.
Am I likely to get any grief from Thai customs because of this? Besides having a return ticket, is there any other way around this if it's likely to be a problem?

No, problem.

You do not need a forward ticket if you have a valid visa.

You do know that you can extend each entry with 30 days at immigrations making it a total of 9 months with two border crossings.

Just be sure to use the last entry before the expire date on the visa.

No, problem.

You do not need a forward ticket if you have a valid visa.

You do know that you can extend each entry with 30 days at immigrations making it a total of 9 months with two border crossings.

Just be sure to use the last entry before the expire date on the visa.

Thanks for the fast reply.

I wasn't aware about the extra 30 days per entry - so that's good to know.

so it's possible to get a multiple entry Visa without having a return-ticket?

I was wondering if I should even bother applying for one when I have just a one-way from The Netherlands to Thailand, but it seems like you've done this.

Don't bother with your return ticket. You don't need one.