Most plumbers wont mess with the septic tank. We deal mostly with components inside the house. Did you have a vent pipe in the yard (often looks like a candy cane made of PVC) before the repair but not after? If all he did was replace the line it shouldn't cause a smell inside the house. All plumbing fixtures inside the house should have properly functioning traps. Those traps would create and maintain a water seal against the sewer gases. You should have at least one vent through the roof to equalize pressures within the drainage system. This prevents positive pressures within the system (caused by fixtures discharging into the lines, ie toilet flush) from pushing gas out through the traps, and negative pressures (the waste in line will pull air behind it like your finger over the end of a straw) from sucking water out of the traps.
Last night my kitchen sink decided to start draining slowly so I paid a guy on taskrabbit to come out and unclog the issue... yeah no. he made a mess dripping black slime everyplace and left me with a sink that not only did not drain, but now the piped leaked! YAY thanks! I learned my lesson, im trusting real plumbers from now on :/ texted them at 11pm and they were able to come out first thing this morning. Fixed the clog, cleared the pipes out, and replaced our hot mess cluster of pipes from the previous owner with one clean new pvc pipe.
In Ireland, a 4-year apprenticeship plus qualification exam was necessary for someone to practice professionally. Accreditation of businesses are of great help in order to show their credibility and experience in the job. Providing emergency call out service was one of advantage of a plumbing business in the area offering 24/7 service, anytime, anywhere.