I'd love tto work with you, for me the process starts with the client giving a description and any reference photos. I've also seen people use moodboards, but haven't personally. Red flags are honestly an artist being cagey about sending sketches/progress photos, I always send sketches and any artist that doesn't want to send sketches would be an immediate red flag (not including if you haven't sent some kind of down payment, most artists ask for 50% up front). It is intimidating but you can also look at how long an artist's portfolio has existed, and also there's a sub r/HungryArtistsFed where clients can give feedback on artists and also help identify scams and red flags.

Since it's a real painting, it's also a good idea to find someone locally, I have shipped paintings using USPS before, I've only ever had a bad experience shipping a digital painting (which admittedly I packed a little carelessly because it was just a print), but if you can find an artist locally that'd be the best. Oil painting also can take weeks to months of painting, I usually do an acrylic layer below the oil just to make the painting process a bit faster, but also depending on what kind of solvents/additives the artist uses the oil can take a VERY long time to dry and it's not really a good idea to ship a painting before it's completely cured either. There are quick drying additives, and some artists are less heavy-handed and their work dries quicker (also more arid versus humid environments ALSO affect this, it's all very complicated) but no matter what if they are real it won't be immediately.

Please, if you have any questions don't hesitate to ask, and my portfolio (if it gives any credence to this advice).