As others have said, it does depend on the business, but generally, I would say don't do it. Having said that, we did offer a free one-week trial when we were doing call answering, but as that was a service, people were more likely to pay once they saw the benefits of it.
As APA Secretarial, I did offer to do a couple of typing jobs for free near the beginning, but what usually happens is the person uses you for the free bit and then you never see them again.
There is a story (I don't know how true it is) of a lady who wanted her book typed. To check the firm's quality of work, she insisted on them typing a chapter for free. They did this and then never heard from her again. It was supposedly the case that she got a different chapter typed by a different firm, so she got the booked typed for free.
Nowadays, I wouldn't offer things for free, unless there is a very good chance of the ROI (as in the free trial with call answering). As APA we won't do free typing, and I wouldn't coach someone for free either.
Look at it this way, would you really offer to replace someone's doors for free, in the hope they'll then get you to do the windows, fascias and soffits? Probably not, because of the overheads involved. Well, no matter what your costs (whether it's pennies or hundreds of pounds) the principle is the same.
Another thing to be careful of is never purchase any sort of hardware or machinery, specific to one client unless they pay for it up front!
We had a client that we used to send out several thousand letters every few months. To keep the costs down he used to provide the labels, however, these were on tractor-feed paper and didn't go through a laser printer very easily and the labels would get screwed up in the printer, sometimes occasionally even leading to having to purchase a new drum unit. After the third time he hired us, I mentioned that it would be much easier and quicker if we purchased a tractor-feed printer (there was an old dot matrix one that was only about £150, would have fitted the bill perfectly). Much to my surprise, there was no argument or discussion from the client, he simply said to go ahead. I added that obviously, as we were purchasing it especially for his job and would have no other need for it, we would have to pass the costs onto him. Again, he said no problem. I was a little taken aback and so, a few days later, I sent him an invoice for the cost of the printer. We never heard from him again!
Thankfully, I hadn't actually purchased it, something in the way he was too happy to accept the cost struck me as odd, especially as he was trying to keep the costs down elsewhere - like supplying the labels. So I was waiting for him to pay us BEFORE I got the printer (I hadn't told him this).
