Why would they not be able to fulfil a user’s order? Problems with liquidity? I highly doubt it. Could they maybe use this part of their TOS as an excuse to limit certain orders at certain price ranges that might not be aligned with their best interests? Who knows?
I think it's about the liquidity at this point. Supposing the network is way too congested, reflecting the transaction only prevents you from placing other ones while you a wait a confirmation on the other hand supposing it's a service within it's terms. I'm not sure but, this is what I could deduce from that.Or simply they don't have how to fulfill it, probably they are running a new improved version of the classical "no your keys, not your coins" upgraded to "everything if ours and we can take it when we want it".
On top of everything else that was mentioned I had a look at the so-called "Cryptocurrency Service - Risk Statement". I don't know who wrote this but probably deep inside he is one crypto hater
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Unlike most currencies, which are backed by governments or other legal entities, or by commodities such as gold or silver,
Can you buy bolivars on skrill? 
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The cryptocurrency market is highly susceptible to market manipulation and other misuse for illegal activities.
More generally, cryptocurrencies are susceptible to bubbles or loss of confidence (irrational or otherwise), which could collapse demand relative to supply.
Accordingly, a hack is likely to lead to substantial depletion of the Supported Cryptocurrency held on your behalf (see below). Whilst the Cryptocurrency Exchange may be willing to compensate users for any such loss, they are not obliged to do so.
More generally, cryptocurrencies are susceptible to bubbles or loss of confidence (irrational or otherwise), which could collapse demand relative to supply.
Accordingly, a hack is likely to lead to substantial depletion of the Supported Cryptocurrency held on your behalf (see below). Whilst the Cryptocurrency Exchange may be willing to compensate users for any such loss, they are not obliged to do so.
Anyhow, I don't know why some people still keep on using skrill, from all the services available they are the worse, I've tried enough in my life and skrill probably is better only than Liberty Reserve, and that only because that one went down.
If you want to play with cryptos that you will never own try Revolut, at least the chances of getting not ever seeing your money again are 98, not 99%.