If one can't get to the location of the bassoon is there a way to verify condition? For example are there photos I should request? Last played 7 years ago...
If closest music repair location is over an hour away from the seller and the seller over 6 hour drive from me - how should I manage?
If it is a valuable instrument you might consider hiring a bassoon teacher to go check it out who lives closer to the instrument. There are so many detailed photos you could request, and although they would be useful, the instrument would still have to be taken through its courses (and compared to other instruments) before deciding to buy. When I bought my clarinet long ago it was about that far away, but I had several to try in that city, and I brought my teacher along with. We eventually found a truly awesome R-13, so it was well worth the effort. We based the decision on its ability to nail the opening phrase of the Weber Concertino. Bring your excerpt book, several professional reeds and bocals, a good strobe tuner, and find that one note. Of course try all the notes, but spend time to identify each of the instruments' strong points and compare thusly. Common things to verify would be the low B natural crescendo from pianississimo, a solid, non-fuzzy tenor and middle C sharp sound, the relative ease and clarity playing through the rite of spring opening, sheherezade passages, bolero solo, etc. Also keep in mind after seven years of dormancy the instrument may need an overhaul, which should be discounted from the price if the seller refuses to restore the instrument.
Richard Barber has given you a very good answer. Perhaps not the one you wanted though, so i will add som alternatives.
First, if you are buying a professional level instrument we are talking a major investment (a recent Heckel might be advertised at 40.000 USD or more). In that case, you should absolutely test play the instrument. Any serious seller will arrange for you to receive the instrument and test it before final purchase. All bassoons are different and this might not (or might) be the one for you to play on the rest of your career.
But I guess that is not the case. You sound like a beginner or amateur looking at an affordable price level. It will still be a good sized investment, if not, well, you might be buying a ILO (instrument looking object). You are still in a situation where you can spend a lot of money on something which will not make you happy. And it is extremely difficult to know from only description and pictures. A picture may help you decide to NOT buy an instrument, but it probably will not be sufficient to help you say yes.
As the instrument has not been played for 7 years, and probably not serviced for quite a few years before that I would budget for an overhaul by a competent bassoon technician. I am happy to have one in my home-town Stockholm, but it will not do with just about anyone that happens to service clarinets or similar. Personally I would budget for 1.000 USD for the overhaul.
The first question to ask is about the instrument brand or maker:
Chinese: eg Lark. There were sold, and perhaps are, a number of Chinese instruments that, hmm, varies a lot. From maybe decent to real lemons. In my mind it is better for you to step away from an at least 7 year old Chinese. The risk is very large for a really bad instrument, not even worth repairing.
Well known brands: there are a number of brands of bassoon that are well known. These are generally of good enough quality to be repaired and played. Examples of brands that might be in this group is Fox, Oscar Adler, Puchner, Schreiber, Mollenhaur, and there are more. Do not buy a Heckel (in this price range they are not what you are looking for). Do not buy a Buffet (they can be very good instruments, but unless you really know what you are doing they are a different breed, so called French bassoons, with different key fingerings).
Odd brands: all bets are really out here. Some are hidden gems, some are unplayable.
Second question is about approximate age of the instrument. Instruments made before 1950 or so can be very good, but you need to know quite a bit more to understand if it will work for you. Instruments younger than that can more easily be judged as to conditions from pictures.
Now to general condition of the instrument. All parts should be there. Nothing obviously broken. Occasional loose pads will be fixed in the overhaul. Finger marks around the holes shows that the instrument has been played which is a good thing. If I had the instrument in my hand I would definitely look into the condition of the inside bore of the boot. Removing the bottom cap and the U-tube lets me look here. There should be a rubber lining on the smaller bore. The large bore should be without scratches and in good condition all the way. A typical problem with bassoons is that the wood at the bottom part of the large bore can start to rot. This is expensive to fix (might be worth it though).
Most retailers selling used instruments has pictures on their websites. You could look there to find objects to compare with. Examples are https://www.howarth.uk.com , https://www.doublereed.co.uk, http://www.millermarketingco.com/previously_owned/. Ebay is difficult because the sales vary between very serious and total scams. You might look at https://www.musicalchairs.info/bassoon/sales (private sells of mainly professional level or odd instruments)
If the seller was a practicing bassoonist, you could request a video of him playing it.
But this sounds as if the seller isn't a player. It's not even a matter of whether you trust him, quite likely HE doesn't know how good the instrument is!
So, send someone to check it out, or take a risk.
