I haven't seen any info on this. There are a lot of .PDS and .AI files that are given away on Dribbble by the creators, but no one seems to state how they can be used. Does anyone know if it's okay to use these for commercial purposes?
practically every freebie I've seen on Dribbble does have this information from the creator. I would take @Joonas' advice in the comments about ones that do not mention it. The ones that do, follow their instructions to a "t".
If you are specifically looking for commercial use, you should search for public domain or Creative Commons licenses in your searches. I'm not sure if they'll be useful in a Dribbble search, but very helpful in typical search via your search engine of choice.
Also to extend this further on the suggested but some come packaged with a file, like many items that are downloaded digitally, a
README.txt file, displays what can and cant be done with the file.
Since that is said I think you should contact the user if you're unsure by clicking their name because I don't know of one member that doesn't have a way you can contact them.