I Presume these friends also know you?
so either..
a) They also know what job you do??
If yes then they have chosen not to ask your advice for a reason personal to them...
so don't interfere with their decisions about who does what to what standard in their home...
or..
b) They don't know what trade you are in??
In which case it is perfectly normal to raise to a point in conversation
and point out a few of your concerns about safety and standards etc..
and offer your services to them should they want it..
(slightly off topic but ref comment in post #4)
Additionally there is nothing wrong with doing work for friends and/or family
providing you keep it all formal just as you would with any other customer...
Before I started self employment I read various books and this point came up a few times in the guides to running a small business..
If you start trying to run a two-tier charges structure and operating model for your jobs....
(close friends -vs- non friends)
it can become very messy when friends of friends ask for work from word of mouth recommendations..
they have been told by your friend you only charge £x.xx per hour...
but you then go and charge this friend of a friend £y.yy per hour!!
he thinks he's been ripped off.... so its best to keep your charges the same...
or you make a rod for your own back!
(had this problem myself many years ago, though I was doing someone a favour...
but they went and told their friends how good and cheap I was!!!!!)
IF you want to do special deals for close friends note it down as a discount..
So they still know what your normal hourly rate is and that they have had a reduction.
opcorn