UIA's (User-Issued Assets) are created by people (and companies), so you are correct in the sense that you must trust the entity that creates that token. Don't buy it if you don't trust them.
MPA's (aka: Smartcoins) are owned by the graphene chain itself and is pegged to a real-world asset via the Bitshares Witness nodes for tokens such as bitUSD, bitEUR, bitARS, bitSilver and more (http://cryptofresh.com/assets).
BlockPay doesn't care which digital currency you use, as it supports them all, and enables the merchant to accept one or more of them at zero cost. This includes UIA's, Smartcoins, Bitcoins, Ethereum, Dash, Litecoin, Dogecoin, Steem Dollars.....
but those open.x are using centralized gateway... isn't it?Blockpay accept Bitcoins on BitShares network I guess then that merchant should trust open.btc gatekeeper right?
Yes, you are correct that assets like Open.EUR , Open.BTC are Bitshares UIA issued by OpenLedger and should have the same amount of backing in a bank account or cold storage. This is the typical exchange counterparty risk that you have with any Bank or Bitcoin exchange.
However with BlockPay the standard configuration is that merchants get MPA, so BitEUR, BitUSD etc. that only have the BitShares blockchain as counterparty. You will always keep your BitEUR even when BlockPay, OpenLedger or any other party goes bankrupt. This is why we decided to primarily use MPA´s and give our users the total control over their money.
In this way, BlockPay is also completely different to other bitcoin payment processors like Coinbase or BitPay that manage the merchant funds. We have no access to the funds at all.
cheers Chris
Then BTC will use bitBTC and it will certainly help BitShares price I guess. But ETH has no bitETH , will BitShares make bitETH, bitDASH if there are high demand?
The BlockPay platform will exchange BTC to BitEUR in the standard setting. The merchant can choose which currency they want to receive at the end. IF the merchant really wants BitETH, he could get it, but the markets needs to exist first.