I've the opportunity to get this 3 sets of HPotter:

 

4720 at 90

As these are retired sets, see what they sell for now checking the "sold listings" on ebay, if you can double your money, then after fees you make money. Are these sets going up in value, are they staying the same, are you investing or looking for a quick buck?

The prices are not bad if you wanted to buy for yourself but they are not great prices, it all depends what you think about harry potter lego and the fture of it, the total is 230 euro, as an investment, buying sets that will retire this year will very probably see a better increase on your money. However, these sets are scarce to find new in sealed boxes so you'd be acquiring something quite rare. If you use the brickpicker price quide you can see how the price has flutated over the past year.

Judging from the data provided for sales in the U.S on 4720 has seen an increase in the last year and that was only $12, the other 2 sets have stayed pretty much exactly the same. Really you need advice from someone who has a closer eye on selling Harry Potter, there are lots of sales for "used" sets so obviously people are still collecting. These sets could double in price in a couple of years, maybe not, there are safer options. Have a look on bricklink for availability and prices, a lego set no one else has for sale new will fetch plenty of $$$$

Looking on bricklink there is nothing special about these prices, also nobody is asking a sky high price for them. If you want to buy for yourself, nothing wrong with buying, as an investment GO PLAY THE MARKET INSTEAD!