Down the years, I've had several occasions when someone wanted me to help them do something and I waved it off for some random reason just so I wouldn't do what they wanted, and as an introvert, this has made most of my excuses go on oppose because as someone who's most indoors and hardly goes out, you don't get to know if I'm in or not, doing something or not.
So in a nutshell, my introversion traits have aided my excuses of not wanting to do something for anyone since they don't get to see me to know if my excuses were genuine or not, and one of the most common excuses I usually give people is that I'm busy, which can mean giving you more time or trying to find someone else to help you do it.
A typical example of cases where I've used such excuses was last year when someone that lives around me wanted to get married. He was told I could design wedding flyers, and because he heard I did it for free to the person who recommended me to him, he also came with the mindset that he wouldn't pay.
When he came and stated his preference, I told him how much it would cost him, but then he kept saying, "Why will you be charging me and not doing it for free as a wedding gift to him?" and immediately I sensed he wasn't ready to pay a dime. I told him I couldn't even take any orders because I've got loads of designs I need to design and submit before his wedding day. So, in a nutshell, I asked him to patronize someone else because I'm busy.
In the end, rather than pay the 3000 naira I charged him, he went on to do it elsewhere at a sum of 7,000. I don't care; I already reduced some amount to make it fair as a friend, but then I needed to correct the notion that because we are friends, you won't pay for a skill I use as another stream of income. It doesn't seem right, and had I done it for him for free, it'd become a thing every single one of them would be expecting.
Another aspect where I usually use the excuse that I'm busy to wave off the possibility of doing something is here on Hive Blockchain. As a simple mobile graphic designer, I've seen many friends appreciate my designs and in the process ask me to help them design a thumbnail for their content.
At first, I usually jump on that opportunity and immediately help them with their designs, but I realize only a few of them give me credit as the creator of their thumbnails by the time they publish their content. Personal, I believe a simple recognition will make others aware of my skills and probably give me a task to help them do theirs, even if it's going to be for free like I do for my friends or for a small fee to compensate my workmanship.
I'm sure many of them will read this and probably know my secret, but then I know it'll also serve as an avenue for them to have a change of heart and give me some credit to help promote my skills and put me in the limelight of the opportunity to get recognized and appreciated for the petty skills I've got.
That's about all on my best and most commonly used excuse that I used to get away from doing something, and it was prompted by the WEEKEND EXPERIENCE community writing prompts that were instituted by 
NB: I make use of Quillbot grammar checker features to help correct some of my grammatical and punctuation errors after writing my content by myself.
Thanks for reading through, have a blessed and productive day ahead.