Since we've had our Lance since it was new, I can't add anything to what the others have on a good overall visual inspection for evidence of leaks, mold or mildew. But I would functionally test everything! Each and every light, outlet, faucets, hot water (both gas & electric if it is a dual source), dump valves, refer (all pwr. sources), furnace, AC, manual & electric slide, jacks each and every item on all systems.
Inquire as to where and how the unit was kept when not in use, i.e. outside uncovered in the snow=nfg! Covered, better, under any kind of roof better yet, garage best especially if kept above freezing and unit plugged in. How is was kept when not in use will tell you a lot!
Once you've done that I'd make an offer contingent on a inspection or survey! Make your deal with a deposit with a limited time for this to be completed, say 10days. Have someone lined for this in advance.
I would have someone experienced with RV's (not a salesman) preferably a technician who has TC experience to go over it and write up discrepancies. A person who does boat surveys would be the even better option but might cost a bit more. WHAT you say! The similarities boats have in systems, & leak and structural issues etc make a boat surveyor an excellent choice, IMO and they are used to writing up detailed inspection reports to include "fair market value"! Okay so you're going to drop a little green for either guy, but that could save you from falling in love with a nightmare of expense's and repairs that you won't see.
"She looked pretty good last night about the time they hollered last call"! Okay, so you won't be drinking when looking but it's easy to "fall in love" so to speak and overlook a lot!
Id also inquire about all the original manuals etc., if they don't have them, not good, IMO as it also indicates a lack of attention to keeping important information for the maintenance, etc.
Our 1181 has been problem free as far as big things go. Couple of minor items that were normal use issues, easily remedied overall.
Ask lots of questions about any and all of it, especially if it seems like it's something that you already know or should know. If the B.S. light comes on, well you'll know.
Feel free to p.m. me if I can be of help.
We love our 1181 after 9+years!
Best of luck!