The core mechanism is easy enough: a country extends the right to live there to overseas property portal buyers who invest a qualifying amount in housing. The qualifying amount varies widely between countries, and governments adjust it with limited notice.
One key point divides residence and naturalisation. Residency lets you live locally, usually subject to renewal, while a passport usually demands a long period of residence. A promise of a passport real estate in nessebar bulgaria return for buying property in bursa an apartment is reason for caution.
Beyond the purchase price, programmes carry additional requirements. Frequent requirements involve a police clearance certificate, medical insurance, evidence of sufficient means and a minimum number of days on local soil annually. Overlooking a single condition can cost you the status regardless of the property.
Tax status remains a separate question entirely. Having residency does not necessarily make you liable for local income tax, though living there for most of the year usually will. A number of states rely on a day-count rule, and the effects touch foreign income.
A sensible approach is simple: pick a albena property you would want anyway, and treat the permit as a bonus. These routes close sometimes at short notice, and an apartment bought only for paperwork becomes difficult to let and difficult to sell.