Finances. You need to be good at quick math and be able to make quick decisions. You have to be careful how much you pay for a book, and then keep careful track of the expenses involved in selling it. For instance, when you sell on a website, they’ll take a commission from the sale. In addition, some sites, like eBay, will charge you a listing fee for each book. If you request that your money be deposited via PayPal, then you’ll be charged a transaction fee per book. If you’re not careful, the fees will quickly negate your profits.
I’d stick with Amazon if I were you. All of my Amazon sites only have Amazon affiliate links. If you use Google Adsense display ads on your site, you’re literally taking people away from your site for the sake of just a few cents with these type of ads. If you direct them just to Amazon, then you have a greater chance of earning more money from that click.
I may as well start with something I know well. When I started out as a freelance writer 20 years ago, things were very different. I wrote mostly for magazines, and I had to rely on snail mail to send out drafts and queries. I’d wait weeks for a response from my editors. Not many people had the patience for it, and few stuck around long enough to ever start earning a real income from it.
And there is no need to be nervous about making such a change to your W-4. The withholding allowances you enter into your W-4 do not determine your tax bill, just how much you pay per paycheck. That means it’s perfectly legal to change the withholding allowances on your W-4, provided you claim the correct number of allowances on your actual tax return.
Amazon: Many people don’t realize that Amazon is a haven for third party sellers, including regular Joes and Janes cleaning out their attics and garages. If you plan to sell more than 40 items per month on Amazon, consider registering as a professional seller. You’ll need to pay a $39.99 monthly subscription fee, a referral fee that usually ranges from 6% to 20%, and a $1.35-per-item closing fee for media items. You won’t pay the $0.99-per-item selling fee, however. Alternatively, register as an individual seller. The fee schedule is the same as for professionals, except you do have to pay the selling fee and don’t have to pay the subscription fee.
You could try advertising more, for example, by putting up signs around the neighborhood, posting about it on social media, or having people you know spread the word. You could also try doing it in a different neighborhood that might have friendlier people, or do it in a time and place where there's likely to be a lot of people walking around the area (e.g., near a church before the end of a mass).
Complete errands or tasks for the elderly. Older people often need help with buying groceries, cleaning their home, performing home maintenance, and paying bills. To find clients, contact your local community center or church to find out if anyone needs help. Additionally, you might post an ad in your local classifieds or talk to people you know to find out if they know someone who needs help.