Correcting Keith's answer (you should have read about these details in the terms and conditions of your bank/broker):
Entrustment orders are like a "soft" limit order and meaningless without a validity (which is typically between 1 and 5 days).
If you buy silver at an entrustment price above market price, say
x when the market offer is
m, then parts of your order will likely be filled at the market price. For the remaining quantity there is now a limit, the bank/broker might fill your order over the next 5 days (or however long the validity is) at various prices, such that the overall average price does not exceed
This is different to a limit order, as it allows the bank/broker to (partially) buy silver at higher prices than
x as long as the overall averages is
x or less. In a limit set-up you might be (partially) filled at market prices first, but if the market moves above
x the bank/broker will not fill any remaining quantities of your order, so you might end up (after a day or 5 days) with a partially filled order.
Also note that an entrustment price below the market price and with a short enough validity behaves like a limit price.
The 4th order type is sort of an opposite-side limit price: A stop-buy means buy when the market offer quote goes above a certain price, a stop-sell means sell when the market bid quote goes below a certain price.
Paired with the entrusment principle, this might mean that you buy/sell on average above/below the price you give.
I don't know how big your orders are or will be but always keep in mind that not all of your order might be filled immediately, a so-called partial fill. This is particularly noteworthy when you're in a pro-rata market.