CLUB ANSWER
Are cheap seamless patterns safe for commercial work?
A low price does not make a pattern unsafe. The decisive points are a clear license, a clean source file and a repeat you can verify before production.
Price and permission are separate
Check what the license permits instead of treating price as a quality signal. Club downloads allow personal and commercial end products, while redistribution of the unchanged source remains prohibited.
Inspect the production file
Use the repeat checker, confirm the 8K dimensions and test the tile at its intended scale. A technically verified inexpensive file can be more useful than an expensive preview with unclear boundaries.
Keep a license record
The account download history records which files were obtained during an active membership. Save that record with the project so a client can understand the permitted use later.