how much will i have to pay in taxes for making $20,000 on ebay?

You owe tax on profit, not revenue. You're going to need proof of how much you spent on materials, shipping, etc. in order to calculate how much of the money you received is actually profit. 

There is a high probability that you will get audited, so make sure you have receipts for everything you claim and that they are legitimate business expenses. You cannot deduct "eating out."

If you made a lot of profit, you will owe a lot of tax. You might also owe a penalty for not paying it at the time you earned the money.

When you file your taxes you'll have to claim this as a small business--and most of your expenses to operate this business will be deductible to reduce that amount of tax. It's not just a straight percentage of your profit that you will end up owing. But yes--you WILL owe tax on your sales. You will probably ALSO have to claim this on your state returns and you will probably end up owing SALES tax on some items, depending on what your state requires. 

Get a tax professional to help you with this. OR file online with one of the services like Turbo-Tax or one of the other ones--they ask questions, do your deductions, and calculate your bills/refunds for you. You can also buy a piece of software that does this at your local office-supply store and see how and what you will owe. 

Note:  it doesn't matter if this is a "hobby" or a business. You made the money and you will have to pay the taxes. 

How much was profit after subtracting cost of items sold and all other expenses?  Did you keep records of your expenses?

why would you have to stop ebay?  You still will have made a lot of money.

And btw you have been illegally evading taxes for all those other years.  You owe it whether you get a tax form for the sales or not. 

Hopefully you kept records of your purchases.  You deduct what you paid for items so you only pay tax on the profit...

Watch what you think you can write off for meals. Unless you were traveling out of your area or having a meeting with a customer, it's unlikely that you qualify to write off anything for meals.  You can deduct the cost of the goods, packing materials, shipping, and ebay fees along with any other necessary expenses.  You should look into the other requirements for doing business in your state, such as sales tax collection.

What did you pay for the items that you sold on eBay.

If you bought the items originally for $30,000 and then sold them on eBay for $20,000. That's capital loss you don't pay taxes on a loss. But if you bought the items for $10,000 and you sold them for $20,000 then after deducting the auction fee of eBay and the cost of using PayPal you would pay tax on the difference

If you made $20,000 and have to pay only $6,000, that leaves you with $14,000, so I don't see why you would have to stop.

You MUST subtract your expenses for eBay fees, PayPal fees, etc., and for what it cost you to buy the stuff that you sold on eBay.  This is not even optional.  It is illegal to pay tax on the full amount that you received; you are allowed to pay tax only on the profit (what you received for selling something minus what it cost to buy it and certain expenses).

You are not allowed to subtract (or use in anyway) what you spent eating out, because that it is not an expense of selling stuff on eBay; it is an unrelated personal expense.

After subtracting the costs of selling stuff (such as eBay fees) and the cost of buying the stuff that you sold, you would then pay some fraction of the profit (typically 14-36%, but it depends on how much other income you had in the same year).

You are not required, or even allowed, to pay tax on the full amount that you received.

None.................