Not sure if it applies here, but a few years ago I emailed several Nissan dealers for a service on my Navara stating I wanted a quote for an R2 service as set out by Nissan.
One was substantially cheaper than the rest and the dealer was quite close.
I took it there and noticed the following day that the £80 fuel filter hadn't been changed. When I challenged the service manager about this, saying that it's part of the R2 service schedule he said the chief mechanic had deemed it not necessary to change it.
Hence the lower price service.
Needless to say I never went back.
From my experience, I'd ensure that regardless what they say, you check exactly what each is offering for the money.