Be aware that with SSR's there are conditions to be met for proper operation. Depending on the type of output, ie SCR, TRIAC, zero crossing devices for AC operation, etc, there may be restrictions to the type of load required for proper operation. Some devices will not operate without a minimum load, and others will actually show a high resistance, but not "open-circuit" ( as mentioned by Papabravo ) when off. There are also 3-phase devices and bridge devices, as well as FET based devices.
Often, unless it is for serviceability, or maybe ease of "agency approval" when connecting or controlling mains powered equipment, SSR's are not the cheapest way to do things. Convenient yes, cheap no.
For me, they fall under the old design maxxim of " cheap, fast, good" and you can only get to pick 2 of the 3 options, with the 3rd being what you won't get.