No. All fees are clearly displayed before you confirm any transaction, and there is no penalty for selling at any time.
The costs you should expect are the ones in the published schedule: the annual storage fee (0.5% p.a. gold, 1.0% p.a. silver and platinum, excluding VAT), the transaction commission (1% per market-order trade, 0.5% on savings-order purchases), and the market spread (around 2.0% on average).
Optional services — such as physical delivery or relocating holdings between vaults — carry their own fees, which are always shown before you confirm the request.