There are many fraudulent or counterfeit stamps around.  Many of them are from so-called Autonomous Regions of various countries.  Russia heads the list with fraudulent issues from these regions:

Altai Region
Amurskaya Province
Jewish Autonomous Region
Franz Josef Territory
Autonomous Region of Evenkia
Republic of Kabard-Balkaria
Kamchatka Region
Karachay-Cherkessia
Autonomous Region of Koriakia
Kuril islands
Novosibirsk Islands
Kolguev Island
Kunashir Island
New Land Island
Spitsbergen Island
Republic of Adygea
Republic of Bashkortostan
Republic of Buriatia
Republic of Daghestan
Republic of Ingushetia
Republic of Ichkeria
Republic of Kalmykia
Republic of Karelia
Komi Republic
Mari-El Republic
Republic of Mordovia
Republic of Sakha (Yakutia)
Republic of North Ossetia
Republic of Tatarstan
Republic of Tuva
Republic of Khakasia
Russian Antarctica
Sakhalin Region
Republic of Udmurtia
Republic of Chuvashia
Another group of fake stamps are from Estonian islands.  Any stamps from these islands are fake:  Abruka, Aegna, Aksi, Hiiumaa, Kihnu, Manilaid, Muhu, Osmussaar, Prangli, Ruhnu, Saaremaa, Suur-Pakri, Vaike-Pakri, and Vorms.

Others you may see are Staffa (an uninhabited island near Scotland) and Nagaland, a region of India that does not issue stamps.

There are plenty of real postage stamps available.  There is no need to pay good money for these fakes.