Very welcome Thierry,
In regards to the differences between wholesale and liquidation. May people mistake anything sold in volume as being wholesale, in fact the word "wholesale" is uses so much as a marketing term these days, that many even confuse drop shipping as wholesale.
Wholesale essentially is the brokerage between a manufacturer and a retailer. The manufacturer produces the item, the wholesaler then stocks the item where retailers can then purchase for sale.
Wholesale works on volume, you more you buy, the better the price you can secure, within reason of course.
Liquidation, while selling in volume and offering the same discounted structure, is different because they deal in a variety of stock. Some new, some customer returns, some salvage, some insurance sell offs, in fact there are many types of stock that a liquidator can sell.
This is the key area where people do get into trouble when dealing in the surplus market. They may well be under the impression that they are buying a certain quality, when in fact they are buying a far less quality.
It's a market that can deliver some great rewards over a period of time, and I stress over a period of time. Liquidation should never been seen as a quick money making opportunity, as one load of stock from a single supplier can very well be different form the exact same supplier the next time you order.
You can find that your investment can move around a lot, up on one load, down on the next and so on. That said, my opinion is that most will make money from this method if they buy correctly and measure their success over a longer period of time.
It's an industry where you can never ask too many questions, and the moment someone is hesitant in providing you with an acceptable answer, it's time to start looking for a new supplier!
Excellent lines of communication between suppliers and traders is important in any business, but absolutely paramount in the surplus market.
This subject has been very well canvased on the forum, and I would suggest doing a search for the terms "liquidation" or "surplus" to learn far more. It's information well worth learning if this is a market you are considering using as a supply source.