HILTON HEAD ISLAND -- Reb Boyles remembers opening his property tax bill last year and thinking it must be a mistake.

"It was outrageous," said Boyles, 82. "I said to myself, 'My gosh.' I just couldn't believe it."

Taxes on his second-row lot and house in North Forest Beach on Hilton Head Island had jumped from $2,985 to $8,110.

Boyles and his wife, Gladys, 79, bought the lot at 122 Dune Lane in 1953. First, they built "a little shack" as a vacation home, then they added a second story. In 1990, they bulldozed the house and built a new one -- one story, four bedrooms. They moved into it permanently 10 years ago after retiring from Allendale, where Boyles had been an optometrist.

Like thousands of other Beaufort County residents, the Boyles have been blessed by the area's hot real estate market but cursed by the higher property taxes that come with it. The lot they paid $1,200 for 52 years ago now is valued at $1.2 million. In the past few years alone -- since the previous reassessment in 1998 -- the lot's taxable value has more than tripled.

"We want to stay here," Gladys Boyles said. "We love it. But with these taxes, it's not easy on a fixed income."

For many others, the sticker shock was even worse. Some appraisals increased as much as 800 percent. On Hilton Head Island, 76 percent of properties got higher tax bills; in greater Bluffton, 59 percent.

While the robust real estate market was the main reason for higher assessments, other factors also played a role, a four-month review showed. Checks of about 1,000 properties in 20 neighborhoods on Hilton Head and in greater Bluffton turned up scores of inconsistencies, anomalies and mistakes that also had an impact.

Officials in the Beaufort County Assessor's Office acknowledge that some mistakes were made in last year's reassessment.

After The Packet sent a list questioning about 200 assessments in early September, deputy assessor Robert Reames responded that his office already knew about some of the problems and was correcting them.

Assessors have learned about other errors while reviewing challenges filed by property owners who thought their 2004 assessments were too high, Reames said.

Reames defended the validity of the overall reassessment, however, saying it was easy to go neighborhood by neighborhood and pick nits. Only about 11 percent of the 106,000 appraisals his staff did are being challenged -- not a bad record, he said.

But some private appraisers and Realtors disagree, especially when it comes to assessments on Hilton Head. The procedure the county uses for assessing property doesn't work well on the island, they said.

Like most county governments, Beaufort County uses the "mass appraisal" technique when it reassesses property.

The approach works best with tract housing or in new developments, where lots and houses are similar, and where there's not a mixture of old and new houses, they said.

Mass appraisals are less accurate in places like Hilton Head, a dynamic market with hardly any cookie-cutter housing, they said.

"In a market like ours where there is such a radical difference between first-row ocean and second-row ocean, that's really hard for the computer to generate," said Steve Linsday, a private appraiser on Hilton Head Island.

Real estate agent James Wedgeworth agreed that Hilton Head presents problems for mass appraisals.

"In the 'real world,' it's easy," Wedgeworth said. "It doesn't matter which side of the road you live on. It's not going to work on Hilton Head. Hilton Head is unique."

Reames agreed that a mass appraisal didn't always lead to accurate assessments.

"It's mass appraisal," he said. "Everything is not going to be perfect."

The Assessor's Office has no choice but to use the process, Reames said. Anything else would take too long and be too expensive.