ViaBTC managed to mine block 793858 with fees ranging from 5-65 sat/vb but it had 193 transactions only. I'm guessing those picked up txs with 5 sat/vb probably came from their paid accelerator service.
Not sure but the wide fee range is interesting. If you have time, you can dig in suspicious low fee rate transactions and check their transaction histories to find how much they probably spent to the Paid service of ViaBTC Transaction Accelerator.
I did not make screenshot but the Paid fee when I tested their Paid Service is $53. If you dig those transactions in block 793858, you might find something to confirm their Paid Service's fees which were paid by real users.
The fee for its Paid service, as of writing is 0.0020672
BTC or $53 equivalently. That is very expensive cost.
Paid accelerator service
Transactions
a71288f1dc6a9da53e56c79a16f0bb94540a1d68a618c3c793438ec80ba7ffca
Transaction Size (Current TX Size + Previous Unconfirmed TX Size)
136 Bytes = (136 + 0) Bytes
Payment Type
Total fee
0.0020672 BTC ≈ 53.08 0.002176 BTC