Use escrow services for direct sales. When you are dealing directly with the buyer, make sure that any money that is transferred goes through an escrow service. This will ensure that all checks clear and that you aren't left with a bounced check and no domain. Escrow services may add a few days to a sale and cost you a percentage, but they can save you a lot of heartache.
Many individuals have the habit of collecting attractive domain names but never using them. If so, why not get rid of unused domain names and in the process, make some cash? It is important to understand the whole process of selling domain names. On the outside, the process may look very easy, but unless a trader is well aware of how the whole process works, it is not easy to find a buyer.
That said, my recommended budget for beginners would be $500+. Using this budget you could buy a bunch of high-potential $10 domain names, expired/dropped domain names or a mix of both. It’s very important to invest only what you can afford to lose and treat this as a side hustle till you get the momentum going. As you gain experience, industry expertise and some sales under your belt, you can then consider slowly growing your business into a full-time gig.