Spotahome would appear to provide a competitive alternative to AirBnb and similar sites. However, they levy an extortionate booking fee of over 50%(!) on a month long booking, and this is charged even if you cancel the booking within 24 hours. Their FAQ does not explicitly disclose this, and they are unwilling to make good faith exceptions.
Spotahome is based in Spain, and governed by EU regulations. Note, however, that were a company to charge a fee of 50% in the U.S., this would be considered extreme and not survive a legal challenge.
AirBnb has its own issues, but they are more transparent about fees, and you can also be assured that you'll never be hit with a 600ε fee on an 1,100ε booking!
I recommend steering clear of Spotahome completely.
Recommendation: Avoid! If you're in Portugal, consider idealista.pt instead - but when dealing with a landlord, get everything in writing!