If one needs to buy an earth tester for home, then he/she can visit online portals that sell such devices. Hioki is one such Singapore-based companies that is active in e-retail of such measuring devices. There are many other websites too that sell such testers and ensure the guarantee and warranty.
Yet, one can seek recommendations and suggestions from experienced people and head to some stores that sell these devices. The testing of functioning can be done in front of the customer. Once assured of quality, price, guarantee-period and functioning; the customer can readily buy a tester for domestic use.