Others have given you some great advice so I won't duplicate that. After reading your response to Kent, I'm FLOORED that the other agent would even suggest putting a nylon sock over the end of the dryer hose (IN THE ATTIC no less !) to collect lint.
(Not that you would, but...) please do not even consider that Dangerous, Crazy , and 100% INCORRECT advice.
Some sellers don't understand how they really can "put off" a buyer with certain decisions that they make (or don't make). It's quite normal to think that they may be "pulling something funny" when many times they really are not. Sometimes they are being advised incorrectly and sometimes the decision is solely their own. (It's also hard for other agents to comment since we don't have every single detail of what's going on).
Some owners may feel: "It's been fine since we've been here" or... "It wasn't code when the house was built" and they simply won't make any changes. (Loosing the deal and a qualified buyer over a relatively inexpensive repair or repairs - Especially in this market - is not exactly rational)....
It sounds like your agent is on the ball so, you should be in good hands. (and please post back what the resolution was because quite a few buyers will be going through the same thing and also thinking the same things that you are. (maybe not with a dryer vent specifically, but your situation is similar to many others).
One suggestion is to also find out if the dryer has been moved from another location (where a proper venting system may be currently installed). You may be able to re-locate the dryer when you move in. Depending on the age of the home, it is pretty common to see both Dryer Vents and Bathroom Exhaust fans routed directly into the attic. It was not spelled out / against code when older homes were built - it's just the way some builders "did it" back then. As accidents happen, codes are updated and change.
In addition to Chalfont's code, exhausting a dryer vent into an attic space most likely appears in the ICC- IBC (International Building Code), along with other codes like BOCA which are adopted throughout most of the U.S. (Chalfont Boro follows the IBC 2006 code and IRC codes for residential construction. New Britain Township follows the IRC code. (Not all townships follow the same codes).
My own preference is NOT to vent a dryer where the upright portion of the hose (or hard line) is higher the a few feet above the outlet on the dryer. It can be done - this is just my personal preference (my father is a builder - retired). Sending lint "up and around multiple bends" to vent increases the spots where it can be trapped and cause a fire.
You should also never use "soft" dryer line for an application that runs a long distance - (in fact, that "old flex plastic stuff" is no longer available and has now been replaced with a flexible foil type.
(Plastic dryer line is.... - surprise.... - against most recent codes - although that won't matter, it seems, to your "homeowner"). Running long runs should be done with the rigid , smooth aluminum sections and rigid elbows - especially if you are going "vertical" and through and attic etc.
If the home is what you want, I'd say, don't loose sleep at night. Move in, be happy, re-locate the dryer line (and exhaust fans if they are incorrect as they put a TON of moisture in the attic causing roof problems) and then you will feel safe that it's done correctly. (My thoughts: If you have a seller "like this" and he does agree / finally give in and do the repair, it may be done by the cheapest standards possible and you may wind up re-doing it when you move in anyway.
Good luck with the sale and many happy memories in your home.
Brian Luce ABR, SRS,
Director of Sales
Weidel Realtors - Doylestown