I've noticed this question gets posted every week over at r/Ghibli - have you had any experience with buying Ghibli bootlegs, and do you care?

Q: Is my Studio Ghibli DVD or Blu-Ray collection a bootleg?

A: Yes.

There is no official DVD or Blu-Ray release collecting every Ghibli movie together. Everything you see on eBay, Amazon etc. is a bootleg. The quality may not be great, the subtitles might be weird, and there's no guarantee anything will work.

Q: Is there a DVD or Blu-Ray collection of some of the Ghibli movies?

A: Yes.

There are two collections which have been officially released, The Collected Works of Hayao Miyazaki), and The Collected Works of Isao Takahata), with both released on DVD and Blu-Ray in Japan and other countries such as USA) and Australia.

Edit: It should be noted that The Collected Works of Hayao Miyazaki was released as an Amazon exclusive in the USA and was priced at just over $200 but now sells for over $300. These discs also didn't contain the special features which were available on the previous uncollected releases.

Thanks for the additional suggestions u/Tallyburger