It is a bit complicated nowadays. In my opinion if any manufacturer forbids to sell his products on Ebay etc. that means it is forbidden.
And you have two possibilities:
1. Manufacturer that which is not worldwide famous brand sells products to wholesaler. This wholesaler might sign the contract with manufacturer that he is not going to let customers sell these products on Ebay etc. Then retailer buys products from wholesaler (might sign the contract but rather not) and sells these products on Ebay because he wants to sell as much as he can. If he doesn't sell on Ebay or other auction he needs to sell through online store or physical store. He can even warning form his wholesaler that it is forbidden to sell on Ebay but on the other hand wholesaler doesn't want to loose customer and might turn a blind eye. There is crisis so situation is difficult. Manufacturer may do the same if he found out his product are sold through Ebay.
It mostly depends on how many products you sell as a retailer. If you sell a lot you bring profit to your wholesaler/supplier.
There is situation possible where the manufacturer moved his production to e.g. China (not only just used as example). Then factory in China made more products that manufacturer ordered. This factory looking for wholesalers around the world that want to buy these products. They sell them cheaper than manufacturer. Chinese called these products over stock in my opinion fakes and from manufacturer point of view and not only is obviously illegal. Products might be the same the same materials used the same package the same name.
So there is a wholesaler who decided to buy these products from Chinese factory. This wholesaler might even doesn't know that this might be illegal. I've seen some Chinese sites where was written that offered products are neither genuine nor fakes. This wholesaler will not inform his retailers that products are not allowed to be sold on Ebay (he doesn't know it or he doesn't care).
2. Manufacturer is a worldwide well-known brand. They sell through own network of physical stores and through official online store. Sometimes they allow to sell over stock to be sold legally. But many times it is forbidden and again factory sell products to wholesalers. Yesterday I got offer from some middleman. He offered me stock of worldwide lingerie brand. In description of products was made in Italy but then I was told it is made in Turkey. They might be fakes or "over-stock". You never know. Even official physical stores may sell not really genuine products but what is interesting they might look the same, made of the same materials and the same quality.
To sum up
I guess it sounds complicated but in fact it really is. Because of internet and moving production to Asia it is difficult or impossible to control situation. It is too late
