Are There A Lot Of Fake Bermuda 1875 Overprints?

I was browsing ebay for Scott 13, 14, 15 and I noticed a lot of variation in overprints, including things like thickness, serifs, vertical alignment, even the size of the period. I included photos of a few of them just so you see what I'm talking about. Neither Scott nor Stanley Gibbons mentions different types so it seems a little curious to me. Someone could fake the overprint and the supposed value would multiply several times over. Does anyone know if these overprints are commonly faked and, if so, how could I detect it?

These shouldn't be bought without certificates. There must be hundreds of forgeries made, some in the late 19th. Century and even some today. Without a certificate they are considered forgeries,

Pagoda

Thanks, Pagoda. I'll take that advice.

The simple rule is that if they add value then assume they are fake without a cert.