BTC-Arbs.com has not shown a single piece of evidence that there's actual trading going on. No contact information (other than email) either.
This point I agree with. It seems they could post something.
The results they post are simply too good to be true. They claim to have 10 people working for them out of a Geneva office. Just add up the costs for such an operation, in one of the most expensive cities in the world. Then consider that a 2% difference in exchange rates between different exchanges doesn't mean a 2% profit. Since you need both fiat and BTC to make the arbitrage-trade, your profit is already down to half that of the price-difference. Then you need to keep reserves of both fiat and BTC on all exchanges, while not all reserves are used every day.
The results so far have been consistent with their story and strategy. So far there few days that they return around 2%. Typically the yields are around 1% or less. For example yesterday was a .5% day which I easily beat with my scrypt mining.
Often price-differences are predominantly one-way: For example, BTC-e is almost always cheaper than Bitstamp. So it is necessary to wire USD from Bitstamp to your bank account and onward to BTC-e, which can easily take over a week. So a large part of the funds is sitting inactive or is locked up in wire-transfers. The price-difference required to achieve the stated results is several times higher than the actual profit figure. And that's not counting all their operational expenses.
Some visibility into their cash/BTC management would be beneficial to showing if the operation were legit or not. However your argument too is also largely hand waving probably based on some negative experiences. While our accounts are divided into BTC/fiat, we don't have any idea how much BTC as been converted into fiat at any given time. BTC is much faster to transfer than fiat. They also talk about using minor exchanges too, but it isn't clear what those are. Too many unknowns to say anything for sure. Lack of visibility though is a valid concern.