Maybe at one time or at certain shops and auction houses or with provable provenance and makers marks, But I come across a lot of interesting 18th-century pieces that are much larger and sold for less than 1000 euro. Now, yes, as you have not seen the pieces I am referencing you should, of course, take my word with a grain of salt. Also, I openly confess I have limited hands-on experience with 18th century Italian, let alone Venetian pieces so I am not anything but an observant amateur. However, these marks strike me entirely as legitimate. The double marking is most likely representative of silver purity and its placed in two places because they started as two pieces. The holy spirit mark is most likely a town mark and not a makers mark (who am I to question a published expert? No one, so take it for what its worth). My oldest piece of Venetian silver is a spoon circa 1700 and both the bowl and handle have the Lion of St.Mark hallmark since they were separate pieces.
Now if this is a fake, it would most likely be a fairly modern one as most of the fantasy fakes from the early 20th century are usually quite elaborate. They would have been designed to grab the attention of tourists who wanted statement pieces for curio cabinets, these are only special if you are a modern collector. And again an earlier fantasy maker would not have needed to properly hallmark the piece as his customer base would have no idea if it was right or wrong anyway.
Now allow me to reiterate that I am not an expert and these are just my thoughts on the matter. I do think though that as eager as people should be to question if a piece is authentic, don't forget to ask as many questions about why it would be faked. I think it is fair to presume that we have all seen a lot of actual, unquestionable fakes in our lifetimes. How does this hold up to those in your experience?
For what its worth I've enclosed pictures of my spoon if it anyway helps.