The way I see it, seriousness in the beginning practically amounts to nothing. Its by the end / middle of the process that they will get properly invested. Buying a guitar is the easy part. If the person is not interested they could easily sell it off. Selling a cheaper guitar at 20-40% loss is way more pocketable than selling an expensive guitar at similar loss. The mid range used market has some pretty good deals, many come from people who start out with good gear without knowing if they are going to invest time into it.
If you join a class (esp from someone who you know / are recommended cuz of your contacts) the teacher will usually hook you up with a good guitar or might let you rent for a month or two, which should be sufficient to know if you want to get another better guitar.
Also, please note this is the way I learnt to play guitar. I started with a crappy black Givson, then even played a black Yamaha acoustic worth 10k (I don't remember the model, but it could very well be F310) but eventually settled with electric guitar as setting up acoustic guitars need expertise, esp with intonation. The expensive acoustics are intonated fairly well, hence their price (At least thats what my guitarist friends tell me). A friend of mine also showed me a chinese knock off guitar which sounded insanely good, tho I admit it was a case of RNGesus smiling on him lol.
Right now I'm not playing my guitar (have to restring and set it up again, also need to fix the neck of my bass guitar). I bought my electric guitar used for 5k and used bass for 4k, if I do indeed abandon playing guitar I'm fairly certain I could sell it without any depreciation. But, to tap into the potential of used market, one does need to spend time not just playing the guitar, but also learning about what makes it tick.