Difference between commerce and Riba in Islam, Does commerce entails risk?

What's the difference between commerce and RIBA in Islam? Let's take the example of looking for a loan to buy a house. Traditional banks are using Riba because they lend you money, you buy your house, you pay the bank monthly payment with totality exceed the total borrowed. Now a so-called Islamic bank called me and they pretend that they are doing commerce and don't use Riba, but I don't see any. **The principle is this:** **You need to find first a house by yourself**, **then the bank buys it, then sell it to you, then you pay them back** in an exact way like with Riba banks. For me it's **exactly the same thing, they borrow you money with interest**, the bank pretending to do commerce is **risking absolutely nothing**, and in case you can't pay back the house, the bank will take the house !!! Also with this so-called Islamic bank, they charge you 20% of the price of the house, whereas traditional banks charge 3% more (in Europe). which means the bank is making fortunes and lose nothing at all. For me, **the definition of commerce entails risk**, which means, the Islamic bank decides first to buy for example 100 houses with its capital. then looking for a customer, **with the risk of having a house not sold**. any insight, please?