I sold boats for years and owned a few. LET ME GIVE YOU SOME ADVISE! FIRST and important, do you have a proper vehicle with 5 people pulling a boat? V-6 may not "cut" it, i.e., burning motor up, transmission not heavy enough, etc., due to weight. Brochures for boats indicate BOAT WEIGHT ONLY, gas per gallon 7 lbs each, trailer 700 to 1000 lbs., I used 300 for gear, coolers, etc. SECOND CONSIDERATION, 5 people on an 18' boat you DO NOT want this small boat on a BUSY lake, YOUR family will not be happy and dangerous. THIRDLY, have professionally installed trailer "hitch". When you go to have installed you will need to know approximate weight being "pulled".
FIRST TIME, Buy used!!! Why? New boat owners will sell within 2 to 3 years average. Most buy TOO small, as you will find out quickly buying 18', or the anticipated use was NOT as expected, average in America is 50 hours per season. As you look at boats consider useage, i.e., skiing, tubing, cruising, etc. If skiing you need a "Larger Engine", not a 4 cylinder or small outboard.
Where to buy? Go, FIRST, to Marinas that "house" boats for clients. Usually they have large buildings where they "fork lift" boats "one row" at a time. If an owner is doing this they more than likely care about the boat by keeping out of weather. These facilities also offer regular maintenance and service. You will find from the "operators" of these facilities boat owners selling.
Boat dealers do sell used but, from my personal experience working at dealers, finding boats traded in are usually not in great shape and sold "as is". You will find boats on "consignment" where owners that could not sell have dealers put on their lots, these are usually over priced because the owner has a minimum they will take, plus the dealer wants a share as well.
There is an abundance of boat owners selling. When you are "prospecting" REMEMBER, the year of the boat is LAST TWO digits of VIN. NOW you know how to tell. If VIN is "scraped" or "missing", DO NOT BUY, it is easy to "steal" boats and one indicator is NO VIN, located on right rear.
Boat dealers use NADA for trade values or resale. As you are shopping review or "get" one of these. Bayliner can be great first boats, they are "cheapest" and as you ride in other makes you will understand why. "Things" start happening with Bayliner after a couple of years.
With only $18,000 you are more than likely looking at a 2 to 3 year old or earlier. More than likely someone "just" ready to get "rid of because they "bought too small" and ready to upgrade.
Hope this helps. DO NOT become boat poor. ANY USED BOAT PAY A QUALIFIED TECH TO INSPECT, APPROX. $150 TO $200, regardless of what you are told. AGAIN, have a proper VEHICLE!
Good Luck, Boating is a Great Family Activity.
Sold Boats in North Atlanta for many years.