There are far too many fakes about and its essential you test your card on receipt, some fakes will pass some of the test programmes, so test with ChkFlsh, Crystal Disk Mark & especially H2testW. H2testW tests the full capacity of the card, so will catch any using aliasing to fake larger than real capacity. A card with full capacity but high error rate/slow write speed indicates a 'ghost run' fake.
I`ve added images to the product gallery to assist in visually identifying genuine & fake cards.
A 32GB card should have a formatted capacity of around 30GB, format in FAT/FAT32 only (NTFS shortens life of flash media & wont improve performance)
A class 4 card must have a write speed of 4MB/s minimum (large files) the first result in Crystal Disk Mark should indicate that.
Read speeds should be over 12MB/s.