Yeah it is to some extent...

If you extract the file you bought, you will find the listed files in the directories they are supossed to be in.
Like "V4Lashes1.jpg" or "V4Teeth.jpg" have to be located in "RuntimeTextures..." because if you load some mat pose it is the Texture folder where Poser will look for the needed textures.
Same with " Body-1 INJ.png" and "Body-1 INJ.pz2" where the .png is the thumbnail for the .pz2 file. To see and use them, you have to put them in your LibrariesPose folder within your Runtime folder.

The PSD files are useful if you have an application that can read PSD files. Like Softimage XSI or Adobe Photoshop.

You can open them and use them to create your own textures or modify existing ones.
For example you can use "lips2.psd" to replace lips coming with some texture that you got already.

But if you don't want to use XSI or PS or similar apps and if you don't want to make your own skins and the like, you may ask the merchant to exchange that product with something else in his store or make use of the refund option.
In one of the manuals that come with Poser you will find a description of filetypes and where they have to be. It's not very complicated after some time.And of all similar applications Poser is by far the easiest to use.
You should also have a look at your installation and what filetypes you find in which folder.
This will give you some idea of where to copy any future content. If you got many products you maybe want to sort them in a different way than what they r sorted after installation.