Is usury a sin ? (to lend at interest)?

It is condemned by the Bible and I think it constituted one of the main problems between the Jewish people and Christian Europe. Nowadays, this practice has become mainstream, so that everybody is doing it. In the past, any mercantile attitude was forbidden, now they encourage you to get a price reduction and they teach you how to SELL YOURSELF on your resume. Attitudes have changed and this mercantilism will have a very negative impact on the economy (already started) by diminishing the level of trust.