Once you reach a certain level of business success, people will inevitably reach out and ask for favors. Some will ask if they can “pick your brain” over coffee or lunch. Others might ask you to speak at an event. You may even be approached by someone who wants you to be their mentor.

While it’s flattering to be asked, unless people are willing to pay (and many aren’t) these “favors” can add up to be big drain on your time — and your income.

So how do you know when to give your time for free — and when to pass? Here are some tips to help you decide:

You’re doing something new

If you’re launching a new product or service, making it free for a short of period time — or for a limited number of people — can help you gather feedback and make any necessary improvements. It can also help you gather testimonials to use in your marketing.

Perhaps you’ve got great industry knowledge but you’re honing a new skill like public speaking or running workshops. Doing the first few for free, will not only help you gain experience, it will also take the pressure off until your confidence has grown.

Make it clear you’re only doing this for a short time though; if you don’t value your time, others won’t either.

It’s a fair swap

Many of the people who want to “pick your brain” will have valuable experience of their own to share. If this is the case, you might agree to that coffee date — in exchange for an hour of their time. Perhaps they’re brilliant at content marketing, financial planning or public speaking; if they’ve got expertise you’d otherwise have to pay for, giving them some of your time for free could be worth the investment. Just make sure you agree exactly what each of you is going to contribute and when.

I recently taught a podcaster how to do her own PR in exchange for coaching on how to create and launch a podcast. We both invested four hours; she got some incredible media coverage and I launched a successful podcast, so it was a big win for both of us.

It’s good PR

When you’re asked to do something for free, ask yourself if it’s aligned with your business values. In other words: will it help you move closer to your goals?

So if a writing a guest post, giving a podcast interview or speaking at an event will get you in front of the kind of the people you’d love to work with — or help you build a valuable business relationship – you should absolutely do it for free. If not, it’s a “thanks but no thanks.”

It’s also worth remembering that someone who asks for “a bit of advice” could be a potential client. But if you’re not willing to give them a bit of your time, how will they know whether you’re a good fit to work together? Offering a free Skype or telephone consultation (say, 15 minutes) means you can give people an insight into how you work, without feeling like you’re being taken for a ride.

I recently started offering this to everyone who reached out to “pick my brain” by email. Not not only does this save time (it’s much quicker for me to jump on a call for 15 minutes than answer a very specific question on email), it also weeds out time wasters.

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Only a small percentage take up my offer of a free call, but those who do really value my time — making every second of that consultation count. And as they’ve taken the trouble to book in a call, they’re generally pretty serious about making progress — which means they’re far more likely to become a client at some point in the future.

You’re doing something you care about

Most business owners are keen to “give something back,” and mentoring an aspiring entrepreneur or giving free consultancy to a charity you care about can be a great way of doing so. Sadly people don’t always value when they get for free, so if you don’t set clear expectations from the outset, you can end up feeling like a free helpline. Being clear on how much time you can offer, and when — right from the outset — will help prevent any misunderstandings.