I believe my hot water baseboard heater was hooked up wrong. The feed and return are opposite. The plumber said it's not a problem as we'll still get heat. Is that so, because we don't get a lot of heat from the heater. Please advise.
Assuming it's a hot-water baseboard heater, there should be no problem from which way the water goes. It's a rather simple machine (pipe with heat dissipators) so it couldn't care less which direction the hot water is flowing.
What could be an issue is if a bleeder valve was installed on the output side and not the intake side. Typically the intake side would collect more air to bleed.