If they don't take NO for an answer within a reasonable time, about 3 seconds in my book then these muppets are fair game;
You are perfectly entitled to:
String them along, wasting their time and having a good laugh at their expense, as in the above example.
Go around their house and pester them and try to sell them your skills - oh, wait, your skills are actually worth what you're charging, their 'product' isn't, so that wouldn't be fair.
Pass on the details of the last muppet who tried to flog you stuff, then you get one muppet trying to sell to the next, I'd love to see that one!
Just say the 'Boss' isn't in at the moment, and could they phone at 9.00 am when your mobile will actually be switched off.
Ask them to phone the purchasing manager but give them a premium rate number - there are some that start with 07, so that would catch out 90% of muppets. Actually you can take out premium rate numbers and reap the benefits that way. Have a good laugh and make a killing at the same time! Forget tiling, just make a living at 50p a minute whilst people try to sell you stuff you don't need, I like that one! Although I say it myself that is genious!
Try to get them involved in a dodgy pyramid marketing scam. Let's face it if they are gullable enough to be convinced that what they are selling is of any worth, and more so to think that people will fall for it, then they will probably fall for that one as well.
Ask them if they would like to invest with Madoff Securities.
Ask if they will take Woolworth vouchers in payment.
Or, my personal favourite, establish who they are before you give your name, then ask them to call you back. Repeat this process as many times as you wish next time they call to suit you and your twisted mind, trailing the bait as needed. Explain that there is a marketing budget and their product sounds interesting but you have to discuss it with the CEO before the next board meeting. The beauty of this trick is that it diverts their attention from people who don't have the time to speak to them.