when I taught quilt-in-a-day classes, I always had to troubleshoot plastic cheap machines- they just had lots of problems. Now I have about 50 vintage machines that are in good working order, a Babylock Ellisimo gold for embroidery, and a huge Bernina 820. Some of the things I look for(and will be keeping as I thin my herd) are: metal gears and cams, less vibration, easy to oil/clean/detangle, good size bobbin(the Bernina is awesome, the 201/221 are not), and stitch quality. If I need to hem a pair of jeans or resew my purse handle, I go straight to a vintage machine. If I am doing assembly line chain-piecing, I want speed and an easy to see fabric guide/foot edge.
I have found it better to buy the top of the line machine from a prior generation(used but refurbished) than a bottom of the line new machine.

Needle up/down feature, stop/start button, easy feed dog lowering, ability to change foot pressure/height, wide harp, easy button hole stitch, single hole stitch plate, good lights,knee lift, thread cutter, non drop-in bobbin( I hate them as you have to take the whole project out of the machine in order to change the bobbin). I think those are the essentials. Inexpensive accessories help as well.

These are all good suggestions. Another thing to consider is lessons. Will the store provide you with free one on one lessons? If so, how many? My store provides me with as many lessons as I want. There is a specific order she does the lessons in but she has moved away from that order when I have had something specific I wanted to discuss.

And the store I bought my serger from provided me with a free refresher course even 8 years after the initial purchase. I was impressed.

A nice machine is a Janome, they are wonderful and have lots of features, I have a 49360 and a new 12000, I think my janome 49360 is a work horse, never a issue
Good Luck

I have two straight stitch only machines that I use regularly. They both have 9" throats, very important to me. They didn't cost a lot of money. I do have three other machines if I need to do anything else. I haven't used them for years.

I agree. In years past, when sewing machines were all metal, you could buy a cheap machine and it just had fewer features. Now a cheap machine is so cheaply made that it does not hold up and in some cases I have read about doesn't sew correctly out of the box.

I have recently bought 3 older Pfaff machines (10-16 years) on ebay and they sew perfectly. If you check feedback of the sellers it is possible to get some good deals on older machines. Some even offer a year warranty. Of course shipping is on the buyer, but it you live close enough you may be able to take advantage of that offer.

"I have found it better to buy the top of the line machine from a prior generation(used but refurbished) than a bottom of the line new machine.[/QUOTE]

I'm looking for another machine for a different reason. I have a wonderful Bernina Artista 200 that I bought about 10 years ago and which I love! However, I am wanting to get a smaller machine to take to quilt group and classes. I haven't done a lot of research yet, but I think I want to get either a smaller lighter-weight Bernina or a Featherweight. I just can't decide. A couple of people in my quilt group have Featherweights and they are so darn cute and the owners love them. However, if I get another Bernina I have the advantage of the dealer's being nearby and very reliable, as well as the possible convenience of interchangeable feet (not sure about this though as I haven't checked it out) and features like needle-down, etc. I will use it only for piecing for the most part so don't need a large throat, dual feed, or FMQ capabilities.
I'm nervous about buying a lot of money to buy a used machine online and not knowing what I'm getting for sure. I think after we get home from a trip we're taking at the end of the month, I'll get more serious about the search. I know there are many other brands that would fit the bit, but I'll probably stick with Bernina if I don't get a Featherweight. I definitely need to do some research, though. Ah, decisions, decisions!

I would make a list of all the features that I want and include the things you want to do on your machine, then do a comparison list of machines to find one that does exactly what you want it to do. Worked for me. I didn't want all the fancy goo ga stuff that creates more things to repair, but wanted certain features.

The perfect machine for one person might not be the right fit for someone else. Make a list of features you want. Try to be somewhat flexible with your brand perceptions & budget. Pre-owned might also be worthy of consideration. Ask to sew on the machine. The right one will feel like a friend. It will make you smile when it shouts "take me home", and every time you use it 😻

To me the most important part of my machine is the service I get from the seller. I have purchased 3 top of the line machines and after having minimum support from the first two I was very careful before purchasing the next machine. My dealer has free classes for learning the software and the machine. She has many classes one can take for quilting, sewing, embroidering. These classes sometimes come with kits that are reasonably priced and the staff will always help you pick out fabric for your project. At least once a year my dealer sponsors a special class. The last one was a foot class. Sure was fun to learn how to use all the different feet. We did not have to purchase these feet unless we wanted to. This gave us a chance to try them first.
When I am having trouble with something I can phone her and she usually can solve the problem over the phone. If not she has a technician that can. Sooo to me SERVICE from my dealer is the most important thing.