Complex sentence: Quidco differs from most cashback sites, in that instead of taking a portion of referral income as commission, the site instead charges a fixed annual membership fee of £5, which is taken out of the first £5 earned by the member.
Split into simpler sentences: Quidco differs from most cashback sites, in that instead of taking a portion of referral income as commission, instead there is a fixed annual membership fee of £5. This is taken out of the first £5 earned by the member.