You know the type - those that say yes to every demand. It's good to keep your customers happy, but that doesn't mean agreeing to everything they ask for. The famous phrase 'the customer is always right' isn't always the case when it comes to painting and decorating.
It doesn't happen very often but there have been instances in the past where customers have demanded I use a product against my recommendation - on one occasion a pink coating for a radiator which consequently faded - but that's something I'm reluctant to do now I have more experience. Now my attitude is 'I'm the professional and I know best'. Customers will usually welcome your expert opinion and it only reflects badly on you if you give in and the finish ends up looking terrible.
This also applies when someone asks you to complete some work that doesn't fall exactly within your remit. At quiet times when jobs are few and far between it can be tempting to take on any work available but make sure you take some time to consider it. The first thing to ask yourself is whether it is a job you can do well and do you have the skills and equipment required? If you're not sure, steer clear and perhaps offer a recommendation if you do know someone that can do the job. The customer will be grateful for your recommendation and remember you next time they need some decorating work doing.
The other point to consider is whether you actually want to be known for doing that job - if someone is asking you to do a bit of painting but also fix the door frames and repair the squeaky floorboards, are you prepared to be recommended to their friends and family as a handy man? Or is painting and decorating what you do best and what you want to stick to? If you're not sure, it could be worth just taking a little time to think about it and in the end, if the job isn't right, don't be afraid to turn it down.