Some services on the deposit/withdrawal page are subject to permanent centralized risk. The reserves that back the said asset can be compromised or stolen. Such as OPEN.BTC, META.BTC, etc...
All services are subject to at least momentary third party risks.
Either way there should be a disclaimer on the withdrawal/deposit page and when someone pulls up the exchange interface when a centralized asset is at least one of the two assets in the trading pair.