Any idea on what I’m doing wrong?
Yeah you're putting the cart before the horse. I sell quite a few custom systems but I certainly don't go building a bunch of computers and advertising them on Craigslist. And heck, I use Craigslist all the time to advertise my repair service and even refurbished desktops and laptops! Custom build clients are different. Let me be frank, cheapwads and custom builds don't mix. It's extremely important to use quality components when building a custom computer but most people just look at the specs and the price and if yours is even a little bit more expensive, they consider it a "bad deal."
You shouldn't be selling custom computers, you should be selling your SERVICE, both the building itself and your consulting service. You don't want the type of client who is looking for the highest specs for the lowest price. Unfortunately that's 95% of people in the custom build space. That is, until they get burnt and come to you to fix the pile of garbage they bought/built.
You'll never be able to compete with garbage builders like CyberPower who use the cheapest garbage Chinese components available and only have a $50 markup. They rely on volume, not customer loyalty, good margins, and repeat business. I have a CyberPower PC in the shop right now. The thing won't boot into Windows. They used some cheap ass ADATA SSD and it's failed after only 14 months. Color me surprised. But this client only saw the high specs and the low price and hit the BUY NOW button without hesitation. Now it's my job to educate them on the turd they bought, replace the low quality garbage components, and create loyalty between me and my client. This client will always come to me in the future if they need service on their current build and when it's time to build a new system. But if I had tried to capture this client BEFORE they got burned, I probably wouldn't have been able to.
I build an average of 3-5 custom systems per week. I keep one or two on hand at any given time and I also stock a good amount of parts. My main shop sells 10x the number of custom systems that I do personally from my home and a crap ton of parts as well. I actually don't sell parts from my home. I only use the parts in repairs/builds. Despite the fact that I could afford to build a bunch of systems and advertise them on Craigslist I don't because I wouldn't see any results from it. I do however get people with custom builds calling me for my repair service that I advertise on Craigslist and I'm sometimes able to build them a new system. I just got in a 1st gen i5 custom build last week and of course I recommended a new build instead of fixing it. The guy wanted me to install an RTX 3080 to improve his gaming performance. Needless to say, I recommended replacing the system.
This guy knew the importance of quality. He had his system built like 12 years ago from a small local shop that's unfortunately gone out of business and they'd already done the work of educating him. It didn't take much to convince him to drop $2,500 on a new build, and he didn't scrutinize every component and complain that he could get a computer with the same specs for cheaper with CyberPower or whatever other garbage "gaming" computer he found on Walmart.com.