How can I make $4500 in the next 48 hours starting with only $800?

1. Start on a Saturday in a large city. You need a car, high speed internet, and an internet-equipped smartphone.
2. Identify the best weekend flea market for antiques in the area. In Los Angeles it may be Long Beach or the Rose Bowl market in Pasadena. Some are the first Sunday of the month, some the second, etc. the Glendale market's also possible.
3. Buy a good flashlight and fresh batteries, a magnifying glass, and a large cloth tote bag. Change your $800 into $20s and $50s.
4. Using high speed internet, go to eBay and browse in the collectible category. Pick an area that interests you or that you have some knowledge about.
5. On the left side of the screen, select "sold items" so you see only the auctions that finished with a successful sale.
6. Sort down in order of final price.
7. Study all the items that sold at above $1000 and read the descriptions closely. Pay special attention to details of maker's name, markings, size, materials. If something especially strikes you, summarize the unique points in the notes function on your phone. If you exhaust that category of collectible, move on to another one.
8. Spend the rest of the day studying. If you have time, visit some large antique stores in the area and get in the mindset of real antiques by looking for pieces in the areas you've studied. The real stuff has a "feel" of genuineness. Don't buy anything yet. Unless you're really really lucky it will all be too expensive.
9. Install the eBay app on your smartphone and familiarize yourself with the search functions.
10. Get a good night's sleep. Get up early. Get to the market when they open (could be 5am) and start looking in the dark with your flashlight.
11. Look for items that are a close match to the pieces you studied up on. Focus on the parts of the market where less professional sellers set up. Stay away from sellers with elaborate tents and tables. Look for amateurs in trucks with lots of stuff.
12. Buy only pieces that match your profile. Try to pay about 10% of the sold prices you studied. For a $2000 value piece, you will pay $200 or less. Get the piece you want into your hands, asking the price as you do so. If it's $500, smile, say thank you, set it down and wait to see what else the seller brings out. You're not experienced enough to buy at that percentage. Don't forget you're a beginner.
13. If the price is close to your limit or below, examine the piece closely and skeptically, not as if you're eager to buy it. If you can, use your smartphone to check the photos of the similar sale you found. Make sure the piece you're looking at is not too clean and bright. Reproductions, especially of pottery and old toys, are common.
14. Then if you're bullish on it, bargain. Offer 75% of the asking price or so. If you get any real price reduction, pay it. If you can't get a price reduction and you're working with a casual, nonprofessional seller--pay the full price. Remember, you're already at 10% of what you think the ultimate value is! Assume that if you set it down someone else will buy it immediately.
15. Keep going until you've spent your bankroll.
16. The action will be over by noon. Go home and examine your finds.

You will make mistakes, because you're a beginner. You may buy a reproduction. You may overpay for something good . You may misjudge the age or markings. But if half the stuff you buy at 10% of eBay value is genuine that means your $800 is worth $4000. To realize the value you may decide to sell on eBay, but for now you have a paper gain. 



Maybe. Don't rely on this to pay your mortgage the first time out.