I saw this coin on the Danish auction site, looked it up on here to find it has a bullion value of ~97 DKK, so I thought I'd take a punt and put in a max bid of 100 DKK - and it turns out I won it for that amount.
It arrived today, but when I weighed it, it only came out as 21g when it should be 25g... diameter is 37.15 mm.
Looked at the date in the star and it looks like it's the 1871 (73) date as well, which would make it worth $400 even in VF according to NGC. That would have made it quite the bargain, so that only reinforces my suspicions.
I've bought quite a few coins from this seller before, and I'm pretty sure he wasn't aware that it was fake. I'm sure he'll refund me when I contact him.
Sent the seller a mail, 5 minutes later the money was in my account - including the postage costs, even though I bought a couple of other coins along with it :-)
The 5 pesetas 1871 with stars 18-73 is the most common counterfeit coin in Spanish numismatic.
It is usually a real coin with 71 in the star, so the magnet test and the weight check doesn't usually work (you are lucky).
The 1 is filing and a 3 is punching. It can be detected with a microscope because the right side of the star is lowered to erase the 1. And with a magnifying glass if the style of the 3 is different of the 7.
The sizes of the 7 and the 3 in your coin are different, and very different of the style in the real coin. Here you can see a photo of the real star.
Referee for Spain, Iberia (ancient), Suebi Kingdom and Visigothic Kingdom